linux-kernel - Re: [BUG REPORT] media: coda: mpeg4 decode corruption on i.MX6qp only

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Date:   Wed, 10 Feb 2021 13:29:29 -0500
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Nicolas Dufresne <nicolas@...fresne.ca>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Adrian Ratiu <adrian.ratiu@...labora.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        linux-media <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG REPORT] media: coda: mpeg4 decode corruption on i.MX6qp only

Found it!

The i.MX6QuadPlus has two pairs of PREs, which use the extended
section of the iRAM. The Classic does not have any PREs or extended
iRAM:

pre1: pre@...8000 {
   compatible = "fsl,imx6qp-pre";
    <snip>
    fsl,iram = <&ocram2>;
};

pre3: pre@...a000 {
    compatible = "fsl,imx6qp-pre";
    <snip>
    fsl,iram = <&ocram3>;
};

The CODA (VPU) driver uses the common section of iRAM:

vpu: vpu@...0000 {
    compatible = "cnm,coda960";
    <snip>
    iram = <&ocram>;
};

The VPU or the PREs are overrunning their assigned iRAM area. How do I
know? Because if I change the PRE iRAM order, the problem disappears!

PRE1: ocram2 change to ocram3
PRE2: ocram2 change to ocram3
PRE3: ocram3 change to ocram2
PRE4: ocram3 change to ocram2

Sven