linux-kernel - Re: [PATCH v5 00/39] i.MX Media Driver

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Message-ID: <20170313081625.GX21222@n2100.armlinux.org.uk>
Date:   Mon, 13 Mar 2017 08:16:25 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Steve Longerbeam <slongerbeam@...il.com>
Cc:     robh+dt@...nel.org, mark.rutland@....com, shawnguo@...nel.org,
        kernel@...gutronix.de, fabio.estevam@....com, mchehab@...nel.org,
        hverkuil@...all.nl, nick@...anahar.org, markus.heiser@...marIT.de,
        p.zabel@...gutronix.de, laurent.pinchart+renesas@...asonboard.com,
        bparrot@...com, geert@...ux-m68k.org, arnd@...db.de,
        sudipm.mukherjee@...il.com, minghsiu.tsai@...iatek.com,
        tiffany.lin@...iatek.com, jean-christophe.trotin@...com,
        horms+renesas@...ge.net.au, niklas.soderlund+renesas@...natech.se,
        robert.jarzmik@...e.fr, songjun.wu@...rochip.com,
        andrew-ct.chen@...iatek.com, gregkh@...uxfoundation.org,
        shuah@...nel.org, sakari.ailus@...ux.intel.com, pavel@....cz,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v5 00/39] i.MX Media Driver

On Sun, Mar 12, 2017 at 09:26:41PM -0700, Steve Longerbeam wrote:
> On 03/12/2017 01:22 PM, Russell King - ARM Linux wrote:
> >What I had was this patch for your v3.  I never got to testing your
> >v4 because of the LP-11 problem.
> >
> >In v5, you've changed to propagate the ipu_cpmem_set_image() error
> >code to avoid the resulting corruption, but that leaves the other bits
> >of this patch unaddressed, along my "media: imx: smfc: add support
> >for bayer formats" patch.
> >
> >Your driver basically has no support for bayer formats.
> 
> You added the patches to this driver that adds the bayer support,
> I don't think there is anything more required of the driver at this
> point to support bayer, the remaining work needs to happen in the IPUv3
> driver.

There is more work, because the way you've merged my changes to
imx_smfc_setup_channel() into csi_idmac_setup_channel() is wrong with
respect to the burst size.

You always set it to 8 or 16 depending on the width:

	burst_size = (image.pix.width & 0xf) ? 8 : 16;

	ipu_cpmem_set_burstsize(priv->idmac_ch, burst_size);

and then you have my switch() statement which assigns burst_size.
My _tested_ code removed the above, added the switch, which had
a default case which reflected the above setting:

	default:
		burst_size = (outfmt->width & 0xf) ? 8 : 16;

and then went on to set the burst size _after_ the switch statement:

	ipu_cpmem_set_burstsize(priv->smfc_ch, burst_size);

The effect is unchanged for non-bayer formats.  For bayer formats, the
burst size is determined by the bayer data size.

So, even if it's appropriate to fix ipu_cpmem_set_image(), fixing the
above is still required.

I'm not convinced that fixing ipu_cpmem_set_image() is even the best
solution - it's not as trivial as it looks on the surface:

        ipu_cpmem_set_resolution(ch, image->rect.width, image->rect.height);
        ipu_cpmem_set_stride(ch, pix->bytesperline);

this is fine, it doesn't depend on the format.  However, the next line:

        ipu_cpmem_set_fmt(ch, v4l2_pix_fmt_to_drm_fourcc(pix->pixelformat));

does - v4l2_pix_fmt_to_drm_fourcc() is a locally defined function (it
isn't v4l2 code) that converts a v4l2 pixel format to a DRM fourcc.
DRM knows nothing about bayer formats, there aren't fourcc codes in
DRM for it.  The result is that v4l2_pix_fmt_to_drm_fourcc() returns
-EINVAL cast to a u32, which gets passed unchecked into ipu_cpmem_set_fmt().

ipu_cpmem_set_fmt() won't recognise that, and also returns -EINVAL - and
it's a bug that this is not checked and propagated.  If it is checked and
propagated, then we need this to support bayer formats, and I don't see
DRM people wanting bayer format fourcc codes added without there being
a real DRM driver wanting to use them.

Then there's the business of calculating the top-left offset of the image,
which for bayer always needs to be an even number of pixels - as this
function takes the top-left offset, it ought to respect it, but if it
doesn't meet this criteria, what should it do?  csi_idmac_setup_channel()
always sets them to zero, but that's not really something that
ipu_cpmem_set_image() should assume.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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