linux-kernel - Re: [PATCH v2 1/7] media: hantro: Set DMA max segment size

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Message-ID: <1564069001.3006.1.camel@pengutronix.de>
Date:   Thu, 25 Jul 2019 17:36:41 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Ezequiel Garcia <ezequiel@...labora.com>,
        linux-media@...r.kernel.org, Hans Verkuil <hans.verkuil@...co.com>
Cc:     kernel@...labora.com,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Tomasz Figa <tfiga@...omium.org>,
        linux-rockchip@...ts.infradead.org,
        Heiko Stuebner <heiko@...ech.de>,
        Jonas Karlman <jonas@...boo.se>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        fbuergisser@...omium.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 1/7] media: hantro: Set DMA max segment size

On Thu, 2019-07-25 at 11:17 -0300, Ezequiel Garcia wrote:
> From: Francois Buergisser <fbuergisser@...omium.org>
> 
> The Hantro codec is typically used in platforms with an IOMMU,
> so we need to set a proper DMA segment size.

... to make sure the DMA-mapping subsystem produces contiguous mappings?

> Devices without an
> IOMMU will still fallback to default 64KiB segments.

I don't understand this comment. The default max_seg_size may be 64 KiB,
but if we are always setting it to DMA_BUT_MASK(32), there is no falling
back.

> Cc: stable@...r.kernel.org
> Fixes: 775fec69008d3 ("media: add Rockchip VPU JPEG encoder driver")
> Signed-off-by: Francois Buergisser <fbuergisser@...omium.org>
> Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
> ---
>  drivers/staging/media/hantro/hantro_drv.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/staging/media/hantro/hantro_drv.c b/drivers/staging/media/hantro/hantro_drv.c
> index b71a06e9159e..4eae1dbb1ac8 100644
> --- a/drivers/staging/media/hantro/hantro_drv.c
> +++ b/drivers/staging/media/hantro/hantro_drv.c
> @@ -731,6 +731,7 @@ static int hantro_probe(struct platform_device *pdev)
>  		dev_err(vpu->dev, "Could not set DMA coherent mask.\n");
>  		return ret;
>  	}
> +	vb2_dma_contig_set_max_seg_size(&pdev->dev, DMA_BIT_MASK(32));

This should be complemented by a call to
vb2_dma_contig_clear_max_seg_size() in _remove,
to avoid leaking dev->dma_parms.

>  
>  	for (i = 0; i < vpu->variant->num_irqs; i++) {
>  		const char *irq_name = vpu->variant->irqs[i].name;

regards
Philipp