linux-kernel - Re: [PATCH v2 8/8] drm: zynqmp_dp: Add debugfs interface for compliance testing

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Date: Thu, 21 Mar 2024 18:31:10 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: Michal Simek <michal.simek@....com>, David Airlie <airlied@...il.com>,
 linux-kernel@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
 linux-arm-kernel@...ts.infradead.org,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 8/8] drm: zynqmp_dp: Add debugfs interface for
 compliance testing

On 21/03/2024 18:08, Sean Anderson wrote:
> On 3/20/24 03:49, Tomi Valkeinen wrote:
>> On 20/03/2024 00:51, Sean Anderson wrote:
>>
>>> +/**
>>> + * enum test_pattern - Test patterns for test testing
>>
>> "for test testing"? =)
>>
>>> @@ -1655,6 +2321,9 @@ static void zynqmp_dp_hpd_irq_work_func(struct work_struct *work)
>>>        u8 status[DP_LINK_STATUS_SIZE + 2];
>>>        int err;
>>>    +    if (READ_ONCE(dp->ignore_hpd))
>>> +        return;
>>> +
>>>        mutex_lock(&dp->lock);
>>>        err = drm_dp_dpcd_read(&dp->aux, DP_SINK_COUNT, status,
>>>                       DP_LINK_STATUS_SIZE + 2);
>>
>> Why do you need READ/WRITE_ONCE() for ignore_hpd?
> 
> It's not protected by dp->lock so we don't have to take it for
> zynqmp_dp_hpd_work_func. Although maybe we should make a version of
> zynqmp_dp_bridge_detect which assumes we already hold the lock.

Does using the macros solve some potential issue, or is it just for 
documenting that this variable is accessed without lock?

  Tomi