linux-kernel - Re: [PATCH v2 0/3] add dma noncoherent API

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Message-ID: <e3hrdrynikmgnyhnbfgs7dqilqxyd2tafrxyfqm6cllka6oo2k@reyomkvbni24>
Date: Mon, 30 Jun 2025 15:28:08 +0800
From: Xu Yang <xu.yang_2@....com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: ezequiel@...guardiasur.com.ar, mchehab@...nel.org, 
	laurent.pinchart@...asonboard.com, hdegoede@...hat.com, gregkh@...uxfoundation.org, 
	mingo@...nel.org, tglx@...utronix.de, 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 v2 0/3] add dma noncoherent API

On Fri, Jun 27, 2025 at 02:25:41PM +0300, Andy Shevchenko wrote:
> On Fri, Jun 27, 2025 at 06:19:36PM +0800, 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
> 
> dma_alloc_noncontiguous()

Okay.

> 
> > 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. Beside, a potential user USB Monitor may read outdated
> > data before the driver do dma sync for cpu which will make the data
> 
> DMA
> CPU

Okay.

> 
> > 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
> 
> DMA
> USB

Okay.

Thanks,
Xu Yang

> 
> > layer will manage synchronization itself.
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>