Re: [PATCH] drm/sun4i: hdmi: add support for ddc-i2c-bus property

From: "Måns Rullgård" <mans@mansr.com>
To: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: David Airlie <airlied@linux.ie>, Chen-Yu Tsai <wens@csie.org>,
	dri-devel@lists.freedesktop.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/sun4i: hdmi: add support for ddc-i2c-bus property
Date: Mon, 11 Mar 2019 16:11:06 +0000	[thread overview]
Message-ID: <yw1xef7d4cit.fsf@mansr.com> (raw)
In-Reply-To: <20190311154702.eslw5ccol44vxcmy@flea> (Maxime Ripard's message of "Mon, 11 Mar 2019 16:47:02 +0100")

Maxime Ripard <maxime.ripard@bootlin.com> writes:

> Hi!
>
> On Mon, Mar 11, 2019 at 01:47:13PM +0000, Mans Rullgard wrote:
>> Sometimes it is desirabled to use a separate i2c controller for ddc
>> access.  This adds support for the ddc-i2c-bus property of the
>> hdmi-connector node, using the specified controller if provided.
>> 
>> Signed-off-by: Mans Rullgard <mans@mansr.com>
>> ---
>>  drivers/gpu/drm/sun4i/sun4i_hdmi.h     |  1 +
>>  drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c | 37 +++++++++++++++++++++++---
>>  2 files changed, 35 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi.h b/drivers/gpu/drm/sun4i/sun4i_hdmi.h
>> index b685ee11623d..b08c4453d47c 100644
>> --- a/drivers/gpu/drm/sun4i/sun4i_hdmi.h
>> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi.h
>> @@ -269,6 +269,7 @@ struct sun4i_hdmi {
>>  	struct clk		*tmds_clk;
>>  
>>  	struct i2c_adapter	*i2c;
>> +	struct i2c_adapter	*ddc_i2c;
>>  
>>  	/* Regmap fields for I2C adapter */
>>  	struct regmap_field	*field_ddc_en;
>> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
>> index 061d2e0d9011..5b2fac79f5d6 100644
>> --- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
>> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
>> @@ -212,7 +212,7 @@ static int sun4i_hdmi_get_modes(struct drm_connector *connector)
>>  	struct edid *edid;
>>  	int ret;
>>  
>> -	edid = drm_get_edid(connector, hdmi->i2c);
>> +	edid = drm_get_edid(connector, hdmi->ddc_i2c ?: hdmi->i2c);
>
> You can't test whether ddc_i2c is NULL or not...
>
>>  	if (!edid)
>>  		return 0;
>>  
>> @@ -228,6 +228,28 @@ static int sun4i_hdmi_get_modes(struct drm_connector *connector)
>>  	return ret;
>>  }
>>  
>> +static struct i2c_adapter *sun4i_hdmi_get_ddc(struct device *dev)
>> +{
>> +	struct device_node *phandle, *remote;
>> +	struct i2c_adapter *ddc;
>> +
>> +	remote = of_graph_get_remote_node(dev->of_node, 1, -1);
>> +	if (!remote)
>> +		return ERR_PTR(-EINVAL);
>> +
>> +	phandle = of_parse_phandle(remote, "ddc-i2c-bus", 0);
>> +	of_node_put(remote);
>> +	if (!phandle)
>> +		return NULL;
>> +
>> +	ddc = of_get_i2c_adapter_by_node(phandle);
>> +	of_node_put(phandle);
>> +	if (!ddc)
>> +		return ERR_PTR(-EPROBE_DEFER);
>> +
>> +	return ddc;
>
> ... Since even in (most) error cases you're returning a !NULL pointer.
>
>> +}
>> +
>>  static const struct drm_connector_helper_funcs sun4i_hdmi_connector_helper_funcs = {
>>  	.get_modes	= sun4i_hdmi_get_modes,
>>  };
>> @@ -575,6 +597,12 @@ static int sun4i_hdmi_bind(struct device *dev, struct device *master,
>>  		goto err_disable_mod_clk;
>>  	}
>>  
>> +	hdmi->ddc_i2c = sun4i_hdmi_get_ddc(dev);
>> +	if (IS_ERR(hdmi->ddc_i2c)) {

... which is checked here.

The property is optional, so the idea was to return null in that case
and use the built-in controller.  If the property exists but some error
occurs, we want to abort rather than proceed with the fallback which
almost certainly won't work.

Maybe I got something wrong in that logic.

-- 
Måns Rullgård