Re: [PATCH v5 1/2] drm/bridge: Add sii902x driver

[Boris Brezillon <boris.brezillon@free-electrons.com>]

Hi Emil,

On Fri, 3 Jun 2016 10:38:49 +0100
Emil Velikov <emil.l.velikov@gmail.com> wrote:

> Hi Boris.
> 
> On 2 June 2016 at 16:00, Boris Brezillon
> <boris.brezillon@free-electrons.com> wrote:
> 
> > +static void sii902x_reset(struct sii902x *sii902x)
> > +{
> > +       if (!sii902x->reset_gpio)
> > +               return;
> > +  
> This is wrong (reset_gpio is err_ptr) although we can/should nuke it
> all together. See below for reasoning.
> 
> > +       gpiod_set_value(sii902x->reset_gpio, 1);
> > +
> > +       msleep(100);  
> Ouch that is some juicy number. Can we get a comment with
> reasoning/origin of it ?

As already explained to Maxime, I just don't know why this is needed,
simply because I don't have access to the datasheet and I just based my
implementation on another driver.
I can add a comment stating that this was extracted from another
implementation, but with no explanation on why this is needed.

Meng, do you have any information about startup-time, or something like
that?

> 
> ...
> 
> > +static void sii902x_bridge_mode_set(struct drm_bridge *bridge,
> > +                                   struct drm_display_mode *mode,
> > +                                   struct drm_display_mode *adj)
> > +{
> > +       u8 buf[HDMI_INFOFRAME_HEADER_SIZE + HDMI_AVI_INFOFRAME_SIZE];  
> HDMI_INFOFRAME_SIZE(AVI) seems shorter/easier to head imho.

Yep.

> 
> > +       struct sii902x *sii902x = bridge_to_sii902x(bridge);
> > +       struct regmap *regmap = sii902x->regmap;
> > +       struct hdmi_avi_infoframe frame;
> > +       int ret;
> > +
> > +       buf[0] = adj->clock;
> > +       buf[1] = adj->clock >> 8;
> > +       buf[2] = adj->vrefresh;
> > +       buf[3] = 0x00;
> > +       buf[4] = adj->hdisplay;
> > +       buf[5] = adj->hdisplay >> 8;
> > +       buf[6] = adj->vdisplay;
> > +       buf[7] = adj->vdisplay >> 8;
> > +       buf[8] = SIL902X_TPI_CLK_RATIO_1X | SIL902X_TPI_AVI_PIXEL_REP_NONE |
> > +                SIL902X_TPI_AVI_PIXEL_REP_BUS_24BIT;
> > +       buf[9] = SIL902X_TPI_AVI_INPUT_RANGE_AUTO |
> > +                SIL902X_TPI_AVI_INPUT_COLORSPACE_RGB;
> > +  
> Since all of the contents are cleared in hdmi_avi_infoframe_pack, move
> the above into const video_data[] ?

Something like

	const video_data[] = {
		adj->clock,
		adj->clock >> 8,
		...
	};

So we would have 2 buffers on the stack? Is this really useful?

> 
> > +       ret = regmap_bulk_write(regmap, SIL902X_TPI_VIDEO_DATA, buf, 10);  
> ... and use ARRAY_SIZE(video_data) over the hardcoded 10 ?
> 
> ...
> 
> > +static int sii902x_bridge_attach(struct drm_bridge *bridge)
> > +{
> > +       struct sii902x *sii902x = bridge_to_sii902x(bridge);
> > +       struct drm_device *drm = bridge->dev;
> > +       int ret;
> > +
> > +       drm_connector_helper_add(&sii902x->connector,
> > +                                &sii902x_connector_helper_funcs);
> > +
> > +       if (!drm_core_check_feature(drm, DRIVER_ATOMIC)) {
> > +               dev_err(&sii902x->i2c->dev,
> > +                       "sii902x driver is only compatible with DRM devices supporting atomic updates");
> > +               return -ENOTSUPP;
> > +       }
> > +
> > +       ret = drm_connector_init(drm, &sii902x->connector,
> > +                                &sii902x_connector_funcs,
> > +                                DRM_MODE_CONNECTOR_HDMIA);  
> Side note: seems like most places in DRM do not check the return value
> (~80 vs ~20). I wonder how badly/likely are things to explode.

Yep. I tend to always check return code, but if you say it's useless
(and error-prone) I can remove it.

> 
> ...
> 
> > +static int sii902x_probe(struct i2c_client *client,
> > +                        const struct i2c_device_id *id)
> > +{  
> ...
> 
> > +
> > +       sii902x->reset_gpio = devm_gpiod_get_optional(dev, "reset",
> > +                                                     GPIOD_OUT_LOW);
> > +       if (IS_ERR(sii902x->reset_gpio))
> > +               dev_warn(dev, "Failed to retrieve/request reset gpio: %ld\n",
> > +                        PTR_ERR(sii902x->reset_gpio));
> > +  
> Documentation says "Required" not optional. The above should be
> updated and one should error out if missing, right ?

Actually I was asked to make it optional, just forgot to update the
documentation. This being said, devm_gpiod_get_optional() returns NULL
if the property is not defined in the DT and an error code if the error
comes from the GPIO layer, so I should just switch back to dev_err()
and return the error code here.

This would make the test in sii902x_reset() valid again.

> 
> ...
> 
> > +
> > +       if (client->irq > 0) {  
> I was always confused which is the correct way to check this >= 0 vs >
> 0. DRM has both :-\
> Do you have any suggestions, should be 'mass convert' DRM to use only
> one of the two ?

Not sure 0 is a valid irq number anymore, so I don't think it's really
important, but I can change it if you want.

Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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