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

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Message-ID: <aF5_td2Bb2vsAJ43@smile.fi.intel.com>
Date: Fri, 27 Jun 2025 14:25:41 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Xu Yang <xu.yang_2@....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 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()

> 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 Beside, a potential user USB Monitor may read outdated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

> 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

> layer will manage synchronization itself.

-- 
With Best Regards,
Andy Shevchenko