[PATCH v3 2/3] drm/st7571-i2c: add support for Sitronix ST7571 LCD controller

[Javier Martinez Canillas]

Marcus Folkesson <marcus.folkesson at gmail.com> writes:

Hello Marcus,

[...]

>> >
>> > A comment for v4:
>> >
>> > I think I will go for a property in the device tree. I've implemented
>> > board entries as above, but I'm not satisfied for two reasons:
>> >
>> > 1. All other properties like display size and resolution are already
>> >    specified in the device tree. If I add entries for specific boards,
>> >    these properties will be somehow redundant and not as generic.
>> >
>> > 2. I could not find a ST7571 with a grayscale display as a off-the-shelf
>> >    product.
>> 
>> Sure, that makes sense to me.
>> 
>> Can I ask if you could still add reasonable default values that could be set
>> in the device ID .data fields ?
>> 
>> As mentioned, I've a ST7567 based LCD and a WIP driver for it. But I could
>> just drop that and use your driver, since AFAICT the expected display data
>> RAM format is exactly the same than when using monochrome for the ST7571.
>> 
>> But due the ST7567 only supporting R1, it would be silly to always have to
>> define a property in the DT node given that does not support other format.
>
> Sure!
> I've looked at the ST7567 datasheet and it seems indeed to be a very similar.
> Both in pixel format and registers are the same.
>

Thanks for confirming, that was my understanding too.

> I think specify a init-function (as those will differ) and constraints will
> be enough to handle both chips.
>
> I will prepare .data with something like this
>
> struct st7571_panel_constraints {
> 	u32 min_nlines;
> 	u32 max_nlines;
> 	u32 min_ncols;
> 	u32 max_ncols;
> 	bool support_grayscale;
> };
>
> struct st7571_panel_data {
> 	int (*init)(struct st7571_device *st7571);
> 	struct st7571_panel_constraints constraints;
> };
>
> struct st7571_panel_data st7571_data = {
> 	.init = st7571_lcd_init,
> 	.constraints = {
> 		.min_nlines = 1,
> 		.max_nlines = 128,
> 		.min_ncols = 128,
> 		.max_ncols = 128,
> 		.support_grayscale = true,
> 	},
> };
>
> static const struct of_device_id st7571_of_match[] = {
> 	{ .compatible = "sitronix,st7571", .data = &st7571_data },
> 	{},
> };
>

That's great! Exactly what I had in mind.

>
> I can add an entry for the ST7567 when everything is in place.
> The chip does not support the I2C interface, so it has to wait until

Yes, but there are designs with carrier boards that support I2C. For
example, I have  [1] and [2]. The former comes with an I2C interface
and uses the ST7567S IC variant, while the latter comes with a 4-wire
SPI interface and uses a ST7567P IC variant.

But don't worry about it. Since I've these displays and your driver now
allows for different IC families after adding the mentioned indirection
layer, it should be very trivial for me to add support for these on top.

> I've split up the driver though, which will be right after this series.
>

Nice, thanks again.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat