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

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Date:   Tue, 27 Jun 2017 23:45:14 +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 Tomasz,
Yeah, the comments are wrong, i will correct it

>> +        */
>> +       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...
>
> 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?
>

Thx for pointing it out ! : )

I looked RGA drvier used in rockchip android and i find it use
kmalloc, so i think it might support separate pages.
I will test it.


> Best regards,
> Tomasz