Barebox OF-Overlay Handling

Barebox OF-Overlay Handling

[Marco Felsch]

Hi there,

I have the following problem. My customer is using overlays for
external devices like: display, camera, etc. The current overlay support
is awesome and most of it works out of the box. There is only one
nitpick: If Barebox isn't build with CONFIG_OF_OVERLAY_LIVE enabled many
error's are printed during boot. Those error's are ignored but let the
user assume that something went really bad:

ERROR: of_resolver: __symbols__ missing from base devicetree
ERROR: of_overlay: fragment 30164b88: phandle 0xffffffff not found
ERROR: of_overlay: fragment 30164c84: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3012fb08: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3012fc34: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3012fd60: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3012fe8c: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3012ffb8: phandle 0xffffffff not found
ERROR: of_overlay: fragment 301300e4: phandle 0xffffffff not found
ERROR: of_overlay: fragment 30130210: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3013033c: phandle 0xffffffff not found
ERROR: of_resolver: __symbols__ missing from base devicetree
ERROR: of_overlay: fragment 30130e94: phandle 0xffffffff not found
ERROR: of_overlay: fragment 30130fc4: phandle 0xffffffff not found
ERROR: of_resolver: __symbols__ missing from base devicetree
ERROR: of_overlay: fragment 30131a14: phandle 0xffffffff not found
ERROR: of_overlay: fragment 301342d4: phandle 0xffffffff not found

The of_firmware_load_overlay() calls triggering those errors.
The error's by itself are correct and I don't wanna change them but the
context must be correct by context I mean:

 - barebox-dt on fpga-platform: An FPGA platform needs a barebox
   base devicetree with __symbols__ and those error are correct because
   the firmware manager needs to load the firmware.
 - barebox-dt on non fpga-platform: Those errors are not correct.
   We don't need __symbols__ for the barebox base devicetree.
 - kernel-dt on any platform: Those error's are correct if
   the overlays are using phandles which should be the case most the
   time.

My proposed solution would be a stub like this:

#ifdef CONFIG_OF_OVERLAY_LIVE
int of_firmware_load_overlay(struct device_node *overlay, const char *path);
#else
static inline int of_firmware_load_overlay(struct device_node *overlay, const char *path)
{
       return 0;
}
#endif /* CONFIG_OF_OVERLAY_LIVE */

The disadvantage of this solution is that it can happen to end in a
non-booting device for FPGA platforms using overlays to programm the
bit stream and forget to enable CONFIG_OF_OVERLAY_LIVE because the
kernel tries to access regions not existing.

I've discussed this with Michael in private but we didn't came to a
conclusion. Therefore I'm asking here any input would be helpfull :)

Regards,
  Marco

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Re: Barebox OF-Overlay Handling

[Rouven Czerwinski]

On Wed, 2021-01-13 at 12:07 +0100, Marco Felsch wrote:
> Hi there,
> 
> I have the following problem. My customer is using overlays for
> external devices like: display, camera, etc. The current overlay support
> is awesome and most of it works out of the box. There is only one
> nitpick: If Barebox isn't build with CONFIG_OF_OVERLAY_LIVE enabled many
> error's are printed during boot. Those error's are ignored but let the
> user assume that something went really bad:
> 
> ERROR: of_resolver: __symbols__ missing from base devicetree
> ERROR: of_overlay: fragment 30164b88: phandle 0xffffffff not found
> ERROR: of_overlay: fragment 30164c84: phandle 0xffffffff not found
> ERROR: of_overlay: fragment 3012fb08: phandle 0xffffffff not found
> ERROR: of_overlay: fragment 3012fc34: phandle 0xffffffff not found
> ERROR: of_overlay: fragment 3012fd60: phandle 0xffffffff not found
> ERROR: of_overlay: fragment 3012fe8c: phandle 0xffffffff not found
> ERROR: of_overlay: fragment 3012ffb8: phandle 0xffffwfffffff not found
> ERROR: of_overlay: fragment 301300e4: phandle 0xffffffff not found
> ERROR: of_overlay: fragment 30130210: phandle 0xffffffff not found
> ERROR: of_overlay: fragment 3013033c: phandle 0xffffffff not found
> ERROR: of_resolver: __symbols__ missing from base devicetree
> ERROR: of_overlay: fragment 30130e94: phandle 0xffffffff not found
> ERROR: of_overlay: fragment 30130fc4: phandle 0xffffffff not found
> ERROR: of_resolver: __symbols__ missing from base devicetree
> ERROR: of_overlay: fragment 30131a14: phandle 0xffffffff not found
> ERROR: of_overlay: fragment 301342d4: phandle 0xffffffff not found
> 
> The of_firmware_load_overlay() calls triggering those errors.
> The error's by itself are correct and I don't wanna change them but the
> context must be correct by context I mean:
> 
>  - barebox-dt on fpga-platform: An FPGA platform needs a barebox
>    base devicetree with __symbols__ and those error are correct because
>    the firmware manager needs to load the firmware.
>  - barebox-dt on non fpga-platform: Those errors are not correct.
>    We don't need __symbols__ for the barebox base devicetree.

I was wondering why you were getting this error even on a platform
without FPGA, turns out of_firmware_load_overlay() is always called if
a devicetree overlay is passed via the DT. This in itself isn't a
problem, but IMO of_firmware_load_overlay() should check first whether
the overlay contains the right compatible ("fpga-region") and property
("firmware-name") before doing of_resolve_phandles and
of_process_overlay. This way we can skip a lot of unnecessary overlay
handling if we don't end up loading a firmware.
 
>  - kernel-dt on any platform: Those error's are correct if
>    the overlays are using phandles which should be the case most the
>    time.

AFAICS this should also fix this case.

> My proposed solution would be a stub like this:
> 
> #ifdef CONFIG_OF_OVERLAY_LIVE
> int of_firmware_load_overlay(struct device_node *overlay, const char *path);
> #else
> static inline int of_firmware_load_overlay(struct device_node *overlay, const char *path)
> {
>        return 0;
> }
> #endif /* CONFIG_OF_OVERLAY_LIVE */

While correct in case all firmware overlays use phandles, in theory
overlays could be purely path-based, with not dependency on the
__symbols__ node. Not sure how common this is.

> The disadvantage of this solution is that it can happen to end in a
> non-booting device for FPGA platforms using overlays to programm the
> bit stream and forget to enable CONFIG_OF_OVERLAY_LIVE because the
> kernel tries to access regions not existing.
> 
> I've discussed this with Michael in private but we didn't came to a
> conclusion. Therefore I'm asking here any input would be helpfull :)

Regards,
Rouven Czerwinski


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Re: Barebox OF-Overlay Handling

[Michael Tretter]

On Wed, 13 Jan 2021 15:07:48 +0100, Rouven Czerwinski wrote:
> On Wed, 2021-01-13 at 12:07 +0100, Marco Felsch wrote:
> > Hi there,
> > 
> > I have the following problem. My customer is using overlays for
> > external devices like: display, camera, etc. The current overlay support
> > is awesome and most of it works out of the box. There is only one
> > nitpick: If Barebox isn't build with CONFIG_OF_OVERLAY_LIVE enabled many
> > error's are printed during boot. Those error's are ignored but let the
> > user assume that something went really bad:
> > 
> > ERROR: of_resolver: __symbols__ missing from base devicetree
> > ERROR: of_overlay: fragment 30164b88: phandle 0xffffffff not found
> > ERROR: of_overlay: fragment 30164c84: phandle 0xffffffff not found
> > ERROR: of_overlay: fragment 3012fb08: phandle 0xffffffff not found
> > ERROR: of_overlay: fragment 3012fc34: phandle 0xffffffff not found
> > ERROR: of_overlay: fragment 3012fd60: phandle 0xffffffff not found
> > ERROR: of_overlay: fragment 3012fe8c: phandle 0xffffffff not found
> > ERROR: of_overlay: fragment 3012ffb8: phandle 0xffffwfffffff not found
> > ERROR: of_overlay: fragment 301300e4: phandle 0xffffffff not found
> > ERROR: of_overlay: fragment 30130210: phandle 0xffffffff not found
> > ERROR: of_overlay: fragment 3013033c: phandle 0xffffffff not found
> > ERROR: of_resolver: __symbols__ missing from base devicetree
> > ERROR: of_overlay: fragment 30130e94: phandle 0xffffffff not found
> > ERROR: of_overlay: fragment 30130fc4: phandle 0xffffffff not found
> > ERROR: of_resolver: __symbols__ missing from base devicetree
> > ERROR: of_overlay: fragment 30131a14: phandle 0xffffffff not found
> > ERROR: of_overlay: fragment 301342d4: phandle 0xffffffff not found
> > 
> > The of_firmware_load_overlay() calls triggering those errors.
> > The error's by itself are correct and I don't wanna change them but the
> > context must be correct by context I mean:
> > 
> >  - barebox-dt on fpga-platform: An FPGA platform needs a barebox
> >    base devicetree with __symbols__ and those error are correct because
> >    the firmware manager needs to load the firmware.
> >  - barebox-dt on non fpga-platform: Those errors are not correct.
> >    We don't need __symbols__ for the barebox base devicetree.
> 
> I was wondering why you were getting this error even on a platform
> without FPGA, turns out of_firmware_load_overlay() is always called if
> a devicetree overlay is passed via the DT. This in itself isn't a
> problem, but IMO of_firmware_load_overlay() should check first whether
> the overlay contains the right compatible ("fpga-region") and property
> ("firmware-name") before doing of_resolve_phandles and
> of_process_overlay. This way we can skip a lot of unnecessary overlay
> handling if we don't end up loading a firmware.

At the moment, the check and firmware load path use the same code path,
because there is no difference except that firmware load requires a resolved
overlay and the check does not. This is a viable solution and there is even a
helper to iterate the fragments and call a check function for each fragment.
However the helper calls find_target, which is responsible for most of the
error messages, and therefore, does not completely resolve the issue.

(Indeed, the check if the fragment has the "fpga-region" compatible is
missing. That's a bug.)

I would rather change the error logging to only log errors if actually
something goes wrong. Because none of the aforementioned errors is actually
fatal from a system perspective, but only from a function perspective.
Furthermore, the messages are not helpful at all to actually find the problem
in case of a unresolved overlay.

>  
> >  - kernel-dt on any platform: Those error's are correct if
> >    the overlays are using phandles which should be the case most the
> >    time.
> 
> AFAICS this should also fix this case.
> 
> > My proposed solution would be a stub like this:
> > 
> > #ifdef CONFIG_OF_OVERLAY_LIVE
> > int of_firmware_load_overlay(struct device_node *overlay, const char *path);
> > #else
> > static inline int of_firmware_load_overlay(struct device_node *overlay, const char *path)
> > {
> >        return 0;
> > }
> > #endif /* CONFIG_OF_OVERLAY_LIVE */

Nack. of_firmware_load_overlay must fail if the overlay describes an
fpga-region. Otherwise the device tree that is passed to the kernel might have
an fpga-region with a firmware-name property and that per specification
requires that the fpga is programmed.

Michael

> 
> While correct in case all firmware overlays use phandles, in theory
> overlays could be purely path-based, with not dependency on the
> __symbols__ node. Not sure how common this is.

> 
> > The disadvantage of this solution is that it can happen to end in a
> > non-booting device for FPGA platforms using overlays to programm the
> > bit stream and forget to enable CONFIG_OF_OVERLAY_LIVE because the
> > kernel tries to access regions not existing.
> > 
> > I've discussed this with Michael in private but we didn't came to a
> > conclusion. Therefore I'm asking here any input would be helpfull :)
> 
> Regards,
> Rouven Czerwinski
> 
> 

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Re: Barebox OF-Overlay Handling

[Michael Tretter]

On Wed, 13 Jan 2021 15:52:23 +0100, Michael Tretter wrote:
> On Wed, 13 Jan 2021 15:07:48 +0100, Rouven Czerwinski wrote:
> > On Wed, 2021-01-13 at 12:07 +0100, Marco Felsch wrote:
> > > Hi there,
> > > 
> > > I have the following problem. My customer is using overlays for
> > > external devices like: display, camera, etc. The current overlay support
> > > is awesome and most of it works out of the box. There is only one
> > > nitpick: If Barebox isn't build with CONFIG_OF_OVERLAY_LIVE enabled many
> > > error's are printed during boot. Those error's are ignored but let the
> > > user assume that something went really bad:
> > > 
> > > ERROR: of_resolver: __symbols__ missing from base devicetree
> > > ERROR: of_overlay: fragment 30164b88: phandle 0xffffffff not found
> > > ERROR: of_overlay: fragment 30164c84: phandle 0xffffffff not found
> > > ERROR: of_overlay: fragment 3012fb08: phandle 0xffffffff not found
> > > ERROR: of_overlay: fragment 3012fc34: phandle 0xffffffff not found
> > > ERROR: of_overlay: fragment 3012fd60: phandle 0xffffffff not found
> > > ERROR: of_overlay: fragment 3012fe8c: phandle 0xffffffff not found
> > > ERROR: of_overlay: fragment 3012ffb8: phandle 0xffffwfffffff not found
> > > ERROR: of_overlay: fragment 301300e4: phandle 0xffffffff not found
> > > ERROR: of_overlay: fragment 30130210: phandle 0xffffffff not found
> > > ERROR: of_overlay: fragment 3013033c: phandle 0xffffffff not found
> > > ERROR: of_resolver: __symbols__ missing from base devicetree
> > > ERROR: of_overlay: fragment 30130e94: phandle 0xffffffff not found
> > > ERROR: of_overlay: fragment 30130fc4: phandle 0xffffffff not found
> > > ERROR: of_resolver: __symbols__ missing from base devicetree
> > > ERROR: of_overlay: fragment 30131a14: phandle 0xffffffff not found
> > > ERROR: of_overlay: fragment 301342d4: phandle 0xffffffff not found
> > > 
> > > The of_firmware_load_overlay() calls triggering those errors.
> > > The error's by itself are correct and I don't wanna change them but the
> > > context must be correct by context I mean:
> > > 
> > >  - barebox-dt on fpga-platform: An FPGA platform needs a barebox
> > >    base devicetree with __symbols__ and those error are correct because
> > >    the firmware manager needs to load the firmware.
> > >  - barebox-dt on non fpga-platform: Those errors are not correct.
> > >    We don't need __symbols__ for the barebox base devicetree.
> > 
> > I was wondering why you were getting this error even on a platform
> > without FPGA, turns out of_firmware_load_overlay() is always called if
> > a devicetree overlay is passed via the DT. This in itself isn't a
> > problem, but IMO of_firmware_load_overlay() should check first whether
> > the overlay contains the right compatible ("fpga-region") and property
> > ("firmware-name") before doing of_resolve_phandles and
> > of_process_overlay. This way we can skip a lot of unnecessary overlay
> > handling if we don't end up loading a firmware.
> 
> At the moment, the check and firmware load path use the same code path,
> because there is no difference except that firmware load requires a resolved
> overlay and the check does not. This is a viable solution and there is even a
> helper to iterate the fragments and call a check function for each fragment.
> However the helper calls find_target, which is responsible for most of the
> error messages, and therefore, does not completely resolve the issue.
> 
> (Indeed, the check if the fragment has the "fpga-region" compatible is
> missing. That's a bug.)

This is wrong. The overlay does not have the "fpga-region" compatible. Only
the target node determines if an overlay targets an fpga-region or not.

Michael

> 
> I would rather change the error logging to only log errors if actually
> something goes wrong. Because none of the aforementioned errors is actually
> fatal from a system perspective, but only from a function perspective.
> Furthermore, the messages are not helpful at all to actually find the problem
> in case of a unresolved overlay.
> 
> >  
> > >  - kernel-dt on any platform: Those error's are correct if
> > >    the overlays are using phandles which should be the case most the
> > >    time.
> > 
> > AFAICS this should also fix this case.
> > 
> > > My proposed solution would be a stub like this:
> > > 
> > > #ifdef CONFIG_OF_OVERLAY_LIVE
> > > int of_firmware_load_overlay(struct device_node *overlay, const char *path);
> > > #else
> > > static inline int of_firmware_load_overlay(struct device_node *overlay, const char *path)
> > > {
> > >        return 0;
> > > }
> > > #endif /* CONFIG_OF_OVERLAY_LIVE */
> 
> Nack. of_firmware_load_overlay must fail if the overlay describes an
> fpga-region. Otherwise the device tree that is passed to the kernel might have
> an fpga-region with a firmware-name property and that per specification
> requires that the fpga is programmed.
> 
> Michael
> 
> > 
> > While correct in case all firmware overlays use phandles, in theory
> > overlays could be purely path-based, with not dependency on the
> > __symbols__ node. Not sure how common this is.
> 
> > 
> > > The disadvantage of this solution is that it can happen to end in a
> > > non-booting device for FPGA platforms using overlays to programm the
> > > bit stream and forget to enable CONFIG_OF_OVERLAY_LIVE because the
> > > kernel tries to access regions not existing.
> > > 
> > > I've discussed this with Michael in private but we didn't came to a
> > > conclusion. Therefore I'm asking here any input would be helpfull :)
> > 
> > Regards,
> > Rouven Czerwinski
> > 
> > 

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