Message-ID: <07766e5e-6009-4b8e-8a50-30ba0fe763f5@linux.dev>
Date: Fri, 25 Oct 2024 10:58:00 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
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 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

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