Re: [PATCH 0/3] i.MX8 malloc pool position and 32-bit only DMA

[Andrey Smirnov <andrew.smirnov@gmail.com>]

On Fri, Aug 24, 2018 at 10:15 AM Sam Ravnborg <sam@ravnborg.org> wrote:
>
> Hi Andrey.
>
> > This series is a result of debugging FEC and uSDHC failures on
> > i.MX8MQ. Patches 1 and 2 are pretty straightforward and shouldn't be
> > controversial. Patch 3, OTOH, may or may not be a good way to solve
> > this problem, but it's a good way to start a discussion on the subject
> > which is my main goal here.
> >
> > Feedback is welcome!
> >
> > Thanks,
> > Andrey Smirnov
> >
> > Andrey Smirnov (3):
> >   mci: imx-esdhc: Bail out if DMA address is larger than 32-bits
> >   net: fec: Bail out if DMA address is larger than 32-bits
>
> In the above patches the checks are distributed to the
> users. Are there any reason why we could not centralize this
> check in the dma code?

We definitely can. As Sascha already pointed out this can be folded
into dma_mapping_error().

> As I assume it is everyone that is constrained to the
> 32BIT address space.
>
> And do we really need these checks if we teach
> malloc to only provide memory that is DMA'able?
>

I'd prefer to keep them since I'd rather not have a situation where
there's a chance of silent, hard to detect, failure, since it
manifests in really bizarre ways (in my case Ethernet would stop
working after I would probe eMMC). Also, once all of the error
checking is folded into dma_mapping_error() it wouldn't be that much
of code anyway.

Thanks,
Andrey Smirnov

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