linux-kernel - Re: [PATCH] drm/edid: Dump the EDID when drm_edid_get_panel

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Message-ID: <956de566-d60a-f257-edff-85a2eac06d99@quicinc.com>
Date:   Tue, 25 Oct 2022 13:39:36 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Doug Anderson <dianders@...omium.org>
CC:     <dri-devel@...ts.freedesktop.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        "David Airlie" <airlied@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/edid: Dump the EDID when drm_edid_get_panel_id() has
 an error

Hi Doug

On 10/24/2022 1:28 PM, Doug Anderson wrote:
> Hi,
> 
> On Fri, Oct 21, 2022 at 2:18 PM Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>>
>> Hi Doug
>>
>> On 10/21/2022 1:07 PM, Douglas Anderson wrote:
>>> If we fail to get a valid panel ID in drm_edid_get_panel_id() we'd
>>> like to see the EDID that was read so we have a chance of
>>> understanding what's wrong. There's already a function for that, so
>>> let's call it in the error case.
>>>
>>> NOTE: edid_block_read() has a retry loop in it, so actually we'll only
>>> print the block read back from the final attempt. This still seems
>>> better than nothing.
>>>
>>> Signed-off-by: Douglas Anderson <dianders@...omium.org>
>>
>> Instead of checkinf for edid_block_status_valid() on the base_block, do
>> you want to use drm_edid_block_valid() instead?
>>
>> That way you get the edid_block_dump() for free if it was invalid.
> 
> I can... ...but it feels a bit awkward and maybe not quite how the
> functions were intended to work together?
> 
> One thing I notice is that if I call drm_edid_block_valid() I'm doing
> a bunch of duplicate work that already happened in edid_block_read(),
> which already calls edid_block_check() and handles fixing headers. I
> guess also if I call drm_edid_block_valid() then I should ignore the
> "status" return value of edid_block_read() because we don't need to
> pass it anywhere (because the work is re-done in
> drm_edid_block_valid()).
> 
> So I guess I'm happy to do a v2 like that if everyone likes it better,
> but to me it feels a little weird.
> 
> -Doug

Alright, agreed. There is some duplication of code happening if we use 
drm_edid_block_valid(). I had suggested that because it has inherent 
support for dumping the bad EDID.

In that case, this change LGTM, because in principle you are doing the 
same thing as _drm_do_get_edid() (with the only difference being here we 
read only the base block as opposed to the full EDID there).

Hence,

Reviewed-by: Abhinav Kumar <quic_abhinavk@...cinc.com>