linux-kernel - Re: [RFC][PATCH 2/3] drm/bridge: adv7511: Add 200ms delay on power-on

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Message-ID: <CAKMK7uFAfZNFmfUmH_RAbCRz+Y9UR8zXSuLACcsZu3J-=LVFrg@mail.gmail.com>
Date:   Fri, 25 Nov 2016 07:33:18 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Archit Taneja <architt@...eaurora.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [RFC][PATCH 2/3] drm/bridge: adv7511: Add 200ms delay on power-on

On Fri, Nov 25, 2016 at 1:23 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>> > Daniel, why do we have an API the is clearly related to interrupt handling
>> > but requires the caller to implement a workqueue ?
>>
>> Because in general you need that workqueue anyway, and up to now there was
>> no driver ever who didn't have a work-queue already.
>
> None of the bridge drivers in drivers/gpu/drm/bridge/ have workqueues. They
> call the HPD helpers from a threaded interrupt handler though. Sleeping in
> that context is fine, calling functions that might rely on interrupts from the
> same device to signal completion (such as reading EDID through .get_modes())
> isn't.

Hm, as long as they all use the bit-banging interfaces they'll
probably be all fine. For everyone else you need multiple layers of
work items to make sure you never end up stalling in an interrupt vs.
holding-mode_config.mutex deadlock. So still not convinced we need
this ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch