linux-kernel - Re: [PATCH v5 0/3] add dma noncoherent API

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Message-ID: <2025070932-stifle-squabble-6042@gregkh>
Date: Wed, 9 Jul 2025 12:12:45 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Hans de Goede <hansg@...nel.org>
Cc: Xu Yang <xu.yang_2@....com>, ezequiel@...guardiasur.com.ar,
	mchehab@...nel.org, laurent.pinchart@...asonboard.com,
	hdegoede@...hat.com, mingo@...nel.org, tglx@...utronix.de,
	andriy.shevchenko@...ux.intel.com, viro@...iv.linux.org.uk,
	thomas.weissschuh@...utronix.de, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	imx@...ts.linux.dev, jun.li@....com
Subject: Re: [PATCH v5 0/3] add dma noncoherent API

On Mon, Jul 07, 2025 at 12:02:41PM +0200, Hans de Goede wrote:
> Hi all,
> 
> On 4-Jul-25 11:57, Xu Yang wrote:
> > On architectures where there is no coherent caching such as ARM it's
> > proved that using dma_alloc_noncontiguous API and handling manually
> > the cache flushing will significantly improve performance.
> > 
> > Refer to:
> > commit 20e1dbf2bbe2 ("media: uvcvideo: Use dma_alloc_noncontiguous API")
> > commit 68d0c3311ec1 ("media: stk1160: use dma_alloc_noncontiguous API")
> > 
> > However, it's obvious that there is significant code duplication between
> > these two commits. Besides, a potential user USB Monitor may read outdated
> > data before the driver do DMA sync for CPU which will make the data
> > unreliable.
> > 
> > To reduce code duplication and avoid USB Monitor result unreliable, this
> > series will introduce DMA noncoherent API to USB core. And the USB core
> > layer will manage synchronization itself.
> > 
> > Then the last 2 patches have used the API.
> > 
> > I have tested uvcvideo driver. But I haven't tested stk1160 driver as I
> > don't have such boards. @Ezequiel Garcia, @Dafna Hirschfeld do you have
> > time to test it? Your support on this would be greatly appreciated.
> 
> It seems that patches 1 + 2 are ready for merging now
> (for patch 3 we should probably wait for testing).
> 
> I think that it would be best for both patches 1 + 2 to
> be merged through the USB tree. The changed code in the UVC
> driver is not touched that often so I do not expect any
> conflicts.

Ok, thanks, I'll take them through the USB tree now.

greg k-h