(EXT) Re: [PATCH v2 4/4] drm/bridge: ti-sn65dsi83: Add vcc supply regulator support

[Laurent Pinchart]

Hi Alexander,

On Wed, Oct 13, 2021 at 08:59:22AM +0000, Alexander Stein wrote:
> On Tue, Oct 12, 2021 at 10:43 +0200, Laurent Pinchart wrote:
> > On Tue, Oct 12, 2021 at 08:48:43AM +0200, Alexander Stein wrote:
> > > VCC needs to be enabled before releasing the enable GPIO.
> > > 
> > > Reviewed-by: Sam Ravnborg <sam at ravnborg.org>
> > > Signed-off-by: Alexander Stein <alexander.stein at ew.tq-group.com>
> > > ---
> > >  drivers/gpu/drm/bridge/ti-sn65dsi83.c | 15 ++++++++++++++-
> > >  1 file changed, 14 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > > index 9072342566f3..a6b1fd71dfee 100644
> > > --- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > > @@ -33,6 +33,7 @@
> > >  #include <linux/of_device.h>
> > >  #include <linux/of_graph.h>
> > >  #include <linux/regmap.h>
> > > +#include <linux/regulator/consumer.h>
> > >  
> > >  #include <drm/drm_atomic_helper.h>
> > >  #include <drm/drm_bridge.h>
> > > @@ -143,6 +144,7 @@ struct sn65dsi83 {
> > >  	struct mipi_dsi_device		*dsi;
> > >  	struct drm_bridge		*panel_bridge;
> > >  	struct gpio_desc		*enable_gpio;
> > > +	struct regulator		*vcc;
> > >  	int				dsi_lanes;
> > >  	bool				lvds_dual_link;
> > >  	bool				lvds_dual_link_even_odd_swap;
> > > @@ -647,6 +649,12 @@ static int sn65dsi83_parse_dt(struct sn65dsi83 *ctx,
> > enum sn65dsi83_model model)
> > >  
> > >  	ctx->panel_bridge = panel_bridge;
> > >  
> > > +	ctx->vcc = devm_regulator_get(dev, "vcc");
> > > +	if (IS_ERR(ctx->vcc))
> > > +		return dev_err_probe(dev, PTR_ERR(ctx->vcc),
> > > +				     "Failed to get supply 'vcc': %pe\n",
> > > +				     ctx->vcc);
> > > +
> > >  	return 0;
> > >  }
> > >  
> > > @@ -691,7 +699,11 @@ static int sn65dsi83_probe(struct i2c_client *client,
> > >  	ctx->bridge.of_node = dev->of_node;
> > >  	drm_bridge_add(&ctx->bridge);
> > >  
> > > -	return 0;
> > > +	ret = regulator_enable(ctx->vcc);
> > > +	if (ret)
> > > +		dev_err(dev, "Failed to enable vcc: %i\n", ret);
> > 
> > I think this should move to sn65dsi83_atomic_pre_enable() (and similarly
> > for regulator_disable()) as keeping the regulator enabled at all times
> > will cost power.
> 
> I get your idea. The thing is that unless 1V8 is provided the bridge is not
> even accessible on I2C. So any access to sn65dsi83.regmap without the vcc
> regulator enabled will fail. AFAICS this is not an issue right now, as regmap
> is only used in sn65dsi83_atomic_enable(), sn65dsi83_atomic_disable() and
> sn65dsi83_atomic_pre_enable(), so your sugestion would work, but I'm
> hestitating a bit. The driver then has to ensure all regmap uses are done
> only when vcc is enabled.

Correct, and that's the usual pattern, drivers need to call
pm_runtime_get_sync() before accessing registers. For all you know, even
if the power to the bridge is on, the I2C controller it is connected to
could be suspended.

-- 
Regards,

Laurent Pinchart