linux-kernel - Re: [PATCH v4 1/3] usb: core: add dma-noncoherent buffer alloc and free API

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Message-ID: <aGaJ0fS25bDoLCfH@smile.fi.intel.com>
Date: Thu, 3 Jul 2025 16:46:57 +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 v4 1/3] usb: core: add dma-noncoherent buffer alloc and
 free API

On Thu, Jul 03, 2025 at 06:38:09PM +0800, Xu Yang wrote:
> This will add usb_alloc_noncoherent() and usb_free_noncoherent()
> functions to support alloc and free buffer in a dma-noncoherent way.
> 
> To explicit manage the memory ownership for the kernel and device,
> this will also add usb_dma_noncoherent_sync_for_cpu/device() functions
> and call it at proper time.  The management requires the user save
> sg_table returned by usb_alloc_noncoherent() to urb->sgt.

...

>  	dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> -	if (urb->transfer_buffer_length != 0
> -	    && !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> +	if (!(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> +		if (!urb->transfer_buffer_length)
> +			return ret;

This return ret out of a sudden are quite fragile. Please, move to use return 0
directly where it is supposed to be 0.

...

> +	} else {
> +		if (!urb->sgt)
> +			return ret;

Ditto.

> +		if (dir == DMA_TO_DEVICE)
> +			flush_kernel_vmap_range(urb->transfer_buffer,
> +						urb->transfer_buffer_length);
> +		dma_sync_sgtable_for_device(hcd->self.sysdev, urb->sgt, dir);
>  	}

>  	return ret;

Ditto?

-- 
With Best Regards,
Andy Shevchenko