Hello, On Wed, Apr 09, 2025 at 11:43:54AM +0200, Javier Martinez Canillas wrote: > Marcus Folkesson <marcus.folkes...@gmail.com> writes: > > Hello Marcus, > > [...] > > >> > >> That's a god question, I don't really know... > >> > >> But fbdev does support XRGB8888, which may be another good reason to add > >> it and make it the default format. Yes, it will cause an unnecessary pixel > >> format conversion but the I2C transport is so slow anyways that compute is > >> not the bottleneck when using these small displays. > > > > Hrm, I now realised that I have another issue. > > Not all LCDs that will be attached to the ST7571 controller will be > > grayscale. > > The display I've attached to the ST7571 is a monochrome LCD for example. > > > > Oh, that's very interesting. This means that vendors are using a more capable > IC > (i.e: ST7571) for display controllers + LCD panels board designs, even where > they > could had used a less capable one (i.e: ST7765). That is, using an IC that > supports > 2-bit grayscale when they could just used one that only supported monochrome > pixels. > > From a quick search, I found for example this one from SinoCrystal: > > https://displaysino.com/product_details/SC128128012-V01.html > > > Maybe the right way to do it is to only support XRGB8888 and specify > > if the display is monochrome or grayscale in the device tree. > > > > Or do you have any good suggestions? > > > > I don't know the proper way to handle this, but what I would do is to include > the actual boards as entries in the OF device ID table instead of just the > ICs. > > And then for each entry you can specify what formats are supported, e.g: > > static const uint32_t monochrome_formats[] = { > DRM_FORMAT_XRGB8888, > DRM_FORMAT_R1 > }; > > static const uint32_t grayscale_formats[] = { > DRM_FORMAT_XRGB8888, > DRM_FORMAT_R1 > DRM_FORMAT_R2 > }; > > static const struct of_device_id st7571_of_match[] = { > /* monochrome displays */ > { > .compatible = "sinocrystal,sc128128012-v01", > .data = monochrome_formats, > }, > ... > /* grayscale displays */ > { > .compatible = "foo,bar", > .data = grayscale_formats, > }, > };
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. > > -- > Best regards, > > Javier Martinez Canillas > Core Platforms > Red Hat Best regards, Marcus Folkesson
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