linux-kernel - Re: [PATCH RFT/RFC 24/49] staging: media: zoran: Use DMA coherent for stat

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Date:   Tue, 22 Sep 2020 06:14:06 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Corentin Labbe <clabbe@...libre.com>
Cc:     gregkh@...uxfoundation.org, laurent.pinchart@...net.be,
        mchehab@...nel.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: [PATCH RFT/RFC 24/49] staging: media: zoran: Use DMA coherent
 for stat_com

On Mon, Sep 21, 2020 at 10:19:59AM +0000, Corentin Labbe wrote:
> Instead of using a fragile virt_to_bus, let's use proper DMA coherent
> for the stat_com entry.
> 
> Signed-off-by: Corentin Labbe <clabbe@...libre.com>
> ---
>  drivers/staging/media/zoran/zoran.h        |  2 ++
>  drivers/staging/media/zoran/zoran_card.c   | 20 +++++++++++++-------
>  drivers/staging/media/zoran/zoran_device.c |  3 +--
>  3 files changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/staging/media/zoran/zoran.h b/drivers/staging/media/zoran/zoran.h
> index aa2a8f688a01..8f3faa4eb60f 100644
> --- a/drivers/staging/media/zoran/zoran.h
> +++ b/drivers/staging/media/zoran/zoran.h
> @@ -351,6 +351,8 @@ struct zoran {
>  	unsigned long frame_num;
>  
>  	wait_queue_head_t test_q;
> +
> +	dma_addr_t p_sc;
>  };
>  
>  static inline struct zoran *to_zoran(struct v4l2_device *v4l2_dev)
> diff --git a/drivers/staging/media/zoran/zoran_card.c b/drivers/staging/media/zoran/zoran_card.c
> index 3a7895be3341..a8d23bf126c3 100644
> --- a/drivers/staging/media/zoran/zoran_card.c
> +++ b/drivers/staging/media/zoran/zoran_card.c
> @@ -931,11 +931,15 @@ static int zr36057_init(struct zoran *zr)
>  	zoran_open_init_params(zr);
>  
>  	/* allocate memory *before* doing anything to the hardware in case allocation fails */
> -	zr->stat_com = kzalloc(BUZ_NUM_STAT_COM * 4, GFP_KERNEL);
>  	zr->video_dev = video_device_alloc();
> -	if (!zr->stat_com || !zr->video_dev) {
> +	if (!zr->video_dev) {
>  		err = -ENOMEM;
> -		goto exit_free;
> +		goto exit;
> +	}
> +	zr->stat_com = dma_alloc_coherent(&zr->pci_dev->dev, BUZ_NUM_STAT_COM * sizeof(u32), &zr->p_sc, GFP_KERNEL);

Again, don't write junk coe like this.  Stick to the 80 lines unless
you have a very good reason.