Re: [PATCH v2 1/8] drm/bridge: rgb-to-vga: Support an enable GPIO

[Archit Taneja]

On 10/25/2016 02:29 PM, Chen-Yu Tsai wrote:
> On Tue, Oct 25, 2016 at 4:09 PM, Archit Taneja <architt@xxxxxxxxxxxxxx> wrote:
> > Hi,
> >
> > On 10/20/2016 09:13 AM, Chen-Yu Tsai wrote:
> > > Some rgb-to-vga bridges have an enable GPIO, either directly tied to
> > > an enable pin on the bridge IC, or indirectly controlling a power
> > > switch.
> > >
> > > Add support for it.
> >
> >
> > Does the bridge on your platform have an active/passive DAC, or is it a
> > smarter encoder chip that is capable of doing more? If so, it might be
> > good to have a separate DT compatible string to it, like what's done
> > in the patch titled:
> >
> > drm: bridge: vga-dac: Add adi,adv7123 compatible string
> >
> > so that we can switch to a different driver later if needed.
>
> The chip is GM7123. It is not configurable. It just takes the LCD RGB/SYNC
> signals and converts them to analog. The only things you can change are
> putting it into sleep mode and tweaking the output drive strength by

Is sleep mode the thing that's controlled by this gpio?


> changing the external reference resistor. The latter would be a hardware
> design decision. I would say this qualifies as "dumb".

Yeah, I agree. I'd want feedback from Laurent too, since he had comments
on the usage of the original dumb-vga-dac driver.

> I revisited the board schematics, and the enable GPIO actually toggles
> an external LDO regulator. So this might be better modeled as a regulator
> supply?

If you model it as a regulator, how would you toggle the GPIO on your
platform?

Looking at the chip pin out, there is a 3.3V VDD supply needed for the
chip, so it would be good to have an optional 'power' regulator supply
anyway.

Archit

> Thanks
> ChenYu
>
> > Thanks,
> > Archit
> >
> >
> > > Signed-off-by: Chen-Yu Tsai <wens@xxxxxxxx>
> > > ---
> > >  .../bindings/display/bridge/dumb-vga-dac.txt       |  2 ++
> > >  drivers/gpu/drm/bridge/dumb-vga-dac.c              | 28
> > > ++++++++++++++++++++++
> > >  2 files changed, 30 insertions(+)
> > >
> > > diff --git
> > > a/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt
> > > b/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt
> > > index 003bc246a270..d3484822bf77 100644
> > > --- a/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt
> > > +++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt
> > > @@ -16,6 +16,8 @@ graph bindings specified in
> > > Documentation/devicetree/bindings/graph.txt.
> > >  - Video port 0 for RGB input
> > >  - Video port 1 for VGA output
> > >
> > > +Optional properties:
> > > +- enable-gpios: GPIO pin to enable or disable the bridge
> > >
> > >  Example
> > >  -------
> > > diff --git a/drivers/gpu/drm/bridge/dumb-vga-dac.c
> > > b/drivers/gpu/drm/bridge/dumb-vga-dac.c
> > > index afec232185a7..b487e5e9b56d 100644
> > > --- a/drivers/gpu/drm/bridge/dumb-vga-dac.c
> > > +++ b/drivers/gpu/drm/bridge/dumb-vga-dac.c
> > > @@ -10,6 +10,7 @@
> > >   * the License, or (at your option) any later version.
> > >   */
> > >
> > > +#include <linux/gpio/consumer.h>
> > >  #include <linux/module.h>
> > >  #include <linux/of_graph.h>
> > >
> > > @@ -23,6 +24,7 @@ struct dumb_vga {
> > >         struct drm_connector    connector;
> > >
> > >         struct i2c_adapter      *ddc;
> > > +       struct gpio_desc        *enable_gpio;
> > >  };
> > >
> > >  static inline struct dumb_vga *
> > > @@ -124,8 +126,26 @@ static int dumb_vga_attach(struct drm_bridge *bridge)
> > >         return 0;
> > >  }
> > >
> > > +static void dumb_vga_enable(struct drm_bridge *bridge)
> > > +{
> > > +       struct dumb_vga *vga = drm_bridge_to_dumb_vga(bridge);
> > > +
> > > +       if (vga->enable_gpio)
> > > +               gpiod_set_value_cansleep(vga->enable_gpio, 1);
> > > +}
> > > +
> > > +static void dumb_vga_disable(struct drm_bridge *bridge)
> > > +{
> > > +       struct dumb_vga *vga = drm_bridge_to_dumb_vga(bridge);
> > > +
> > > +       if (vga->enable_gpio)
> > > +               gpiod_set_value_cansleep(vga->enable_gpio, 0);
> > > +}
> > > +
> > >  static const struct drm_bridge_funcs dumb_vga_bridge_funcs = {
> > >         .attach         = dumb_vga_attach,
> > > +       .enable         = dumb_vga_enable,
> > > +       .disable        = dumb_vga_disable,
> > >  };
> > >
> > >  static struct i2c_adapter *dumb_vga_retrieve_ddc(struct device *dev)
> > > @@ -169,6 +189,14 @@ static int dumb_vga_probe(struct platform_device
> > > *pdev)
> > >                 return -ENOMEM;
> > >         platform_set_drvdata(pdev, vga);
> > >
> > > +       vga->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
> > > +                                                  GPIOD_OUT_LOW);
> > > +       if (IS_ERR(vga->enable_gpio)) {
> > > +               ret = PTR_ERR(vga->enable_gpio);
> > > +               dev_err(&pdev->dev, "failed to request GPIO: %d\n", ret);
> > > +               return ret;
> > > +       }
> > > +
> > >         vga->ddc = dumb_vga_retrieve_ddc(&pdev->dev);
> > >         if (IS_ERR(vga->ddc)) {
> > >                 if (PTR_ERR(vga->ddc) == -ENODEV) {
> >
> > --
> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> > a Linux Foundation Collaborative Project

--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project