linux-kernel - Re: [PATCH v6 0/8] drm: zynqmp_dp: IRQ cleanups and debugfs support

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Message-ID: <20cf573c-d05f-444c-9463-f342a750f6cb@ideasonboard.com>
Date: Mon, 28 Oct 2024 17:04:11 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 David Airlie <airlied@...il.com>, Michal Simek <michal.simek@....com>,
 Daniel Vetter <daniel@...ll.ch>, "Sagar, Vishal" <vishal.sagar@....com>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v6 0/8] drm: zynqmp_dp: IRQ cleanups and debugfs support

Hi,

On 25/10/2024 17:58, Sean Anderson wrote:
> Hi Tomi,
> 
> On 10/3/24 10:53, Sean Anderson wrote:
>> On 10/2/24 10:50, Tomi Valkeinen wrote:
>>> Hi,
>>>
>>> On 01/10/2024 21:31, Sean Anderson wrote:
>>>> On 8/9/24 15:35, Sean Anderson wrote:
>>>>> This series cleans up the zyqnmp_dp IRQ and locking situation. Once
>>>>> that's done, it adds debugfs support. The intent is to enable compliance
>>>>> testing or to help debug signal-integrity issues.
>>>
>>> I think the patches 1-7 look fine, and I think I can pick those already to drm-misc if you're ok with that.
>>>
>>> I'm a bit unsure about patch 8, probably mainly because I don't have experience with the compliance testing.
>>>
>>> How have you tested this? With some DP analyzer/tester, I presume?
>>
>> For my test setup I used an oscilloscope hooked up to the displayport
>> output using a fixture that broke the signals out to SMA. Since the
>> oscilloscope cannot emulate a sink, I first had the output connected to
>> a monitor. Then I disabled HPD and reconnected the output to my fixture.
>> This process is described in more detail in the documentation.
>>
>>> I think none of this (patch 8) is needed by almost anybody.
>>
>> Well, I found it very useful for debugging a signal integrity issue I
>> was having. Once I could have a look at the signals it was very clear
>> what the problem was.
>>
>>> Even among zynqmp_dp developers I assume it's very rare to have the
>>> hardware for this. I wonder if it would make sense to have the debugfs
>>> and related code behind a compile option (which would be nice as the
>>> code wouldn't even compiled in), or maybe a module parameter (which
>>> would be nice as then "anyone" can easily enable it for compliance
>>> testing). What do you think?
>>
>> Other drivers with these features just enabled it unconditionally, so I
>> didn't bother with any special config.
>>
>>> I also somehow recall that there was some discussion earlier about
>>> how/if other drivers support compliance testing. But I can't find the
>>> discussion. Do you remember if there was such discussion, and what was
>>> the conclusion? With a quick look, everything in the debugfs looks
>>> generic, not xilinx specific.
>>
>> The last it got discussed was back in [1], but I never got any further
>> response. I agree that some of this is generic, and could probably be
>> reworked into some internal helpers. But I don't have the bandwidth at
>> the moment to do that work.
>>
>> --Sean
>>
>> [1] http://lore.kernel.org/dri-devel/cda22b0c-8d7c-4ce2-9a7c-3b5ab540fa1f@linux.dev
> 
> Does this all make sense to you? At the moment I don't believe I have any
> changes I need to resend for (although this series is archived in patchwork [1]
> for some reason).
> 
> --Sean
> 
> [1] https://patchwork.kernel.org/project/dri-devel/list/?series=878338&archive=both

I was hoping to get tested-by from amd, as I can't test this properly, 
but it's probably pointless to wait.

The biggest hesitation I have is what I mentioned earlier: this adds a 
lot of code which is not for normal use. It would be nice to split this 
into a separate file, maybe behind a compile option, but I fear that'll 
require a more restructuring of the driver.

So, I think it's fine, I'll apply this tomorrow.

  Tomi