linux-kernel - Re: [PATCH 1/5] [media] rockchip/rga: v4l2 m2m support

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Date:   Wed, 28 Jun 2017 08:29:09 +0800
From:   Jacob Chen <jacobchen110@...il.com>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Heiko Stübner <heiko@...ech.de>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>
Subject: Re: [PATCH 1/5] [media] rockchip/rga: v4l2 m2m support

Hi,

2017-06-27 16:39 GMT+08:00 Tomasz Figa <tfiga@...omium.org>:
> Hi Jacob,
>
> Please see my comments inline.
>
> On Mon, Jun 26, 2017 at 11:51 PM, Jacob Chen <jacob-chen@...wrt.com> wrote:
>> Rockchip RGA is a separate 2D raster graphic acceleration unit. It
>> accelerates 2D graphics operations, such as point/line drawing, image
>> scaling, rotation, BitBLT, alpha blending and image blur/sharpness.
> [snip]
>> +static int rga_buf_init(struct vb2_buffer *vb)
>> +{
>> +       struct rga_ctx *ctx = vb2_get_drv_priv(vb->vb2_queue);
>> +       struct rockchip_rga *rga = ctx->rga;
>> +       struct sg_table *sgt;
>> +       struct scatterlist *sgl;
>> +       unsigned int *pages;
>> +       struct rga_buf *buf;
>> +       unsigned int address, len, i, p;
>> +       unsigned int mapped_size = 0;
>> +
>> +       /* Create local MMU table for RGA */
>> +       sgt = vb2_plane_cookie(vb, 0);
>> +
>> +       /*
>> +        * Alloc (2^3 * 4K) = 32K byte for storing pages, those space could
>> +        * cover 32K * 4K = 128M ram address.
>
> Unless I'm missing something, there is 1024 32-bit values in one 4K
> page, which can point to 4 MB of memory. The code allocates 8 of them,
> which in total allows at most 32 MB per buffer.
>
>> +        */
>> +       pages = (unsigned int *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 3);
>
> This is rather unfortunate and you should expect failures here on
> actively used systems with uptime longer than few hours. Changing this
> to dma_alloc_coherent() and enabling CMA _might_ give you a bit better
> success rate, but...
>

I decide to alloc a page pool when driver probe and get page from that poll.

> Normally, this kind of (scatter-gather capable) hardware would allow
> some kind of linking of separate pages, e.g. last entry in the page
> would point to the next page, or something like that. Doesn't this RGA
> block have something similar?
>
> Best regards,
> Tomasz