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

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Message-ID: <20241210142819.GK573@pendragon.ideasonboard.com>
Date: Tue, 10 Dec 2024 16:28:19 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Geert Uytterhoeven <geert+renesas@...der.be>
Cc: Douglas Anderson <dianders@...omium.org>,
	Andrzej Hajda <andrzej.hajda@...el.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Robert Foss <rfoss@...nel.org>, 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

On Tue, Dec 10, 2024 at 03:18:46PM +0100, Geert Uytterhoeven 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.

As I'd like to get a proper solution for this I'm not going to ack this
patch, but I won't nack it either.

> v2:
>   - Use I2C adapter/address instead of ida_alloc().
> ---
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index 9e31f750fd889745..fb452d1b46995673 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -480,6 +480,7 @@ static int ti_sn65dsi86_add_aux_device(struct ti_sn65dsi86 *pdata,
>  				       const char *name)
>  {
>  	struct device *dev = pdata->dev;
> +	const struct i2c_client *client = to_i2c_client(dev);
>  	struct auxiliary_device *aux;
>  	int ret;
>  
> @@ -488,6 +489,7 @@ static int ti_sn65dsi86_add_aux_device(struct ti_sn65dsi86 *pdata,
>  		return -ENOMEM;
>  
>  	aux->name = name;
> +	aux->id = (client->adapter->nr << 10) | client->addr;
>  	aux->dev.parent = dev;
>  	aux->dev.release = ti_sn65dsi86_aux_device_release;
>  	device_set_of_node_from_dev(&aux->dev, dev);

-- 
Regards,

Laurent Pinchart