linux-kernel - Re: [PATCH v2] drm/bridge: ti-sn65dsi86: Fix multiple instances

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Message-ID: <CAD=FV=XpRt_ivSDz0Lzc=A+z3KFrXkVYTn716TD1kZMAyoGQ_A@mail.gmail.com>
Date: Tue, 10 Dec 2024 09:08:52 -0800
From: Doug Anderson <dianders@...omium.org>
To: Geert Uytterhoeven <geert+renesas@...der.be>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Robert Foss <rfoss@...nel.org>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
	Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Linus Walleij <linus.walleij@...aro.org>, Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, 
	Wolfram Sang <wsa+renesas@...g-engineering.com>, 
	Luca Ceresoli <luca.ceresoli@...tlin.com>, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, 
	Greg KH <gregkh@...uxfoundation.org>, dri-devel@...ts.freedesktop.org, 
	linux-renesas-soc@...r.kernel.org, linux-i2c@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/bridge: ti-sn65dsi86: Fix multiple instances

Hi,

On Tue, Dec 10, 2024 at 6:19 AM Geert Uytterhoeven
<geert+renesas@...der.be> wrote:
>
> Each bridge instance creates up to four auxiliary devices with different
> names.  However, their IDs are always zero, causing duplicate filename
> errors when a system has multiple bridges:
>
>     sysfs: cannot create duplicate filename '/bus/auxiliary/devices/ti_sn65dsi86.gpio.0'
>
> Fix this by using a unique instance ID per bridge instance.  The
> instance ID is derived from the I2C adapter number and the bridge's I2C
> address, to support multiple instances on the same bus.
>
> Fixes: bf73537f411b0d4f ("drm/bridge: ti-sn65dsi86: Break GPIO and MIPI-to-eDP bridge into sub-drivers")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> On the White Hawk development board:
>
>     /sys/bus/auxiliary/devices/
>     |-- ti_sn65dsi86.aux.1068
>     |-- ti_sn65dsi86.aux.4140
>     |-- ti_sn65dsi86.bridge.1068
>     |-- ti_sn65dsi86.bridge.4140
>     |-- ti_sn65dsi86.gpio.1068
>     |-- ti_sn65dsi86.gpio.4140
>     |-- ti_sn65dsi86.pwm.1068
>     `-- ti_sn65dsi86.pwm.4140
>
> Discussion after v1:
>   - https://lore.kernel.org/8c2df6a903f87d4932586b25f1d3bd548fe8e6d1.1729180470.git.geert+renesas@glider.be
>
> Notes:
>   - While the bridge supports only two possible I2C addresses, I2C
>     translators may be present, increasing the address space.  Hence the
>     instance ID calculation assumes 10-bit addressing.  Perhaps it makes
>     sense to introduce a global I2C helper function for this?
>
>   - I think this is the simplest solution.  If/when the auxiliary bus
>     receives support à la PLATFORM_DEVID_AUTO, the driver can be
>     updated.
>
> v2:
>   - Use I2C adapter/address instead of ida_alloc().
> ---
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 2 ++
>  1 file changed, 2 insertions(+)

While I agree with Laurent that having a more automatic solution would
be nice, this is small and fixes a real problem. I'd be of the opinion
that we should land it.

Reviewed-by: Douglas Anderson <dianders@...omium.org>

If I personally end up being the person to land it, I'll likely wait
until January since I'll be on vacation soon for the holidays and I
don't want to check something that's slightly controversial in and
then disappear. If someone else feels it's ready to land before then I
have no objections.

-Doug