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

[Doug Anderson]

Hi,

On Tue, Dec 10, 2024 at 6:19 AM Geert Uytterhoeven
<geert+renesas at glider.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 at glider.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 at chromium.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