Re: [PATCH 3/3] media: stk1160: use dma_alloc_noncontiguous API

From: Christoph Hellwig <hch@lst.de>
To: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Cc: ezequiel@vanguardiasur.com.ar, linux-media@vger.kernel.org,
	laurent.pinchart@ideasonboard.com, hverkuil@xs4all.nl,
	ribalda@chromium.org, tfiga@chromium.org, senozhatsky@google.com,
	hch@lst.de, kernel@collabora.com
Subject: Re: [PATCH 3/3] media: stk1160: use dma_alloc_noncontiguous API
Date: Tue, 11 Jan 2022 09:13:31 +0100	[thread overview]
Message-ID: <20220111081331.GB21713@lst.de> (raw)
In-Reply-To: <20220111065505.6323-4-dafna.hirschfeld@collabora.com>

On Tue, Jan 11, 2022 at 08:55:05AM +0200, Dafna Hirschfeld wrote:
> Replace the urb buffers allocation to
> use the noncontiguous API. This improve performance
> on Arm.
> The noncontiguous API require handling
> synchronization.
> This commit is similar to the one sent to
> uvc: [1]

Strange formatting.  I'd flow this as:

Replace the urb buffers allocation to use the noncontiguous API.  This
improve performance on ARM plattform (XXX: insert why here)
The noncontiguous API requires the driver to handle synchronization.
This commit is similar to this one for the uvc driver:

    https://lkml.org/lkml/2021/3/12/1506

> @@ -310,6 +311,9 @@ static void stk1160_isoc_irq(struct urb *urb)
>  		return;
>  	}
>  
> +	dma_sync_sgtable_for_cpu(stk1160_get_dmadev(dev), stk_urb->sgt, DMA_FROM_DEVICE);
> +	invalidate_kernel_vmap_range(stk_urb->transfer_buffer, urb->transfer_buffer_length);

Besisdes the unreadably long lines, I'd invalidate the vmap range before
the direct mapping range.