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

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Message-ID: <ba1eb42c-118f-4afb-bf14-befad68a5945@ideasonboard.com>
Date: Wed, 30 Oct 2024 14:30:18 +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 Sean,

On 28/10/2024 17:04, Tomi Valkeinen wrote:
> 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@...ux.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
> 

Thanks, pushed.

  Tomi