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SubjectRe: [PATCH] drm/sun4i: hdmi: add support for ddc-i2c-bus property
Date
Maxime Ripard <maxime.ripard@bootlin.com> writes:

> On Mon, Mar 11, 2019 at 04:11:06PM +0000, Måns Rullgård wrote:
>> 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.
>
> Indeed, I just got confused. I guess returning ENODEV in such a case,
> and testing for that, would make things more obvious.

There's also a case I hadn't thought of: property exists but isn't a
valid phandle. What do you think is the correct action in that case?

--
Måns Rullgård

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