Re: [RFC PATCH 0/7] usb: dwc2 host driver

[Sascha Hauer <s.hauer@pengutronix.de>]

On Tue, Jan 14, 2020 at 06:12:26PM +0100, Jules Maselbas wrote:
> On Tue, Jan 14, 2020 at 03:27:04PM +0100, Sascha Hauer wrote:
> > Hi Jules,
> > 
> > On Tue, Jan 14, 2020 at 02:21:05PM +0100, Jules Maselbas wrote:
> > > Hi Sascha,
> > > 
> > > I've been working on a driver for the dwc2 otg controller, for both host
> > > and device mode.  Like you I've started from U-Boot driver and I mixed
> > > it with some part from Linux.  For instance I've removed the register
> > > structs and I've been using the same defines for register bit-fields as
> > > in Linux.
> > > 
> > > I would like to share my version of the host driver, as the gadget driver
> > > one still requires some cleanup.  This series is not to be applied on the
> > > driver you proposed. However I am willing to propose a new series that can
> > > be applied on the driver you proposed.  What do you think?
> > 
> > The dwc2 driver was a quick shot, I am all in for improvements. Removing
> > the register structs is very nice and I would be interested in gadget
> > support as well.
> The gadget support is almost ready, I got the dfu gadget working. :)

Well, USB gadget support would be a strong argument for your version ;)

>  
> > What SoC are you using the driver on?
> I am using this driver on our custom SoC, the Kalray Coolidge MPPA (k1c).
> I didn't tried on other SoC.
> 
> > I am not sure if it makes sense to rebase your patches on my driver. If
> > you can convince me that yours is better then we could just remove mine
> > and merge yours instead.
> I don't have a strong argument in favor of my version. Except that I have
> already made some changes over the original U-Boot version: 
> 
> I've tried to improve the roothub interface making it easier to decode
> new requests.
> 
> I have removed the memcpy done in transfer_chunk between the usb data
> buffer and the dma buffer :/
> However this mean that all buffer used for usb tranfert must be dma
> capable.  Not all usb transfers use dma_alloc for it's buffers but
> sometime they are allocated on the stack, this can be problematic if
> the stack cannot be used by DMA.

We do this on other controllers as well, so this shouldn't be a problem.
The day will come we either have to fix the callers or create some
bounce buffer implementation for non DMA capable memory.

Sascha

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