Re: [PATCH v3 2/3] drm/st7571-i2c: add support for Sitronix ST7571 LCD controller
From: Thomas Zimmermann
Date: Tue Apr 08 2025 - 09:58:08 EST
Hi
Am 08.04.25 um 15:20 schrieb Marcus Folkesson:
[...]
+static int st7571_set_pixel_format(struct st7571_device *st7571,
+ u32 pixel_format)
+{
+ switch (pixel_format) {
+ case DRM_FORMAT_C1:
+ return st7571_set_color_mode(st7571, ST7571_COLOR_MODE_BLACKWHITE);
+ case DRM_FORMAT_C2:
+ return st7571_set_color_mode(st7571, ST7571_COLOR_MODE_GRAY);
+ default:
+ return -EINVAL;
+ }
These should be DRM_FORMAT_R1 and DRM_FORMAT_R2 and not C{1,2}. The former
is for displays have a single color (i.e: grey) while the latter is when a
pixel can have different color, whose values are defined by a CLUT table.
I see.
Does fbdev only works with CLUT formats? I get this error when I switch
to DRM_FORMAT_R{1,2}:
[drm] Initialized st7571 1.0.0 for 0-003f on minor 0
st7571 0-003f: [drm] format C1 little-endian (0x20203143) not supported
st7571 0-003f: [drm] No compatible format found
st7571 0-003f: [drm] *ERROR* fbdev: Failed to setup emulation (ret=-22)
For testing purposes, you can add the _R formats to the switch case at
https://elixir.bootlin.com/linux/v6.13.7/source/drivers/gpu/drm/drm_fb_helper.c#L1246
and see how it goes.
Best regards
Thomas
...
+
+static const uint32_t st7571_primary_plane_formats[] = {
+ DRM_FORMAT_C1,
+ DRM_FORMAT_C2,
+};
+
I would add a DRM_FORMAT_XRGB8888 format. This will allow your display to
be compatible with any user-space. Your st7571_fb_blit_rect() can then do
a pixel format conversion from XRGB8888 to the native pixel format.
This were discussed in v2, but there were limitations in the helper
functions that we currently have.
I will look into how this could be implemented in a generic way, but maybe that is
something for a follow up patch?
[...]
+
+static const struct drm_plane_helper_funcs st7571_primary_plane_helper_funcs = {
+ DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
+ .atomic_check = st7571_primary_plane_helper_atomic_check,
+ .atomic_update = st7571_primary_plane_helper_atomic_update,
+};
Maybe you want an .atomic_disable callback that clears your screen ?
Good point, yes, I will add that.
+
+/*
+ * CRTC
+ */
+
+static const struct drm_crtc_helper_funcs st7571_crtc_helper_funcs = {
+ .atomic_check = drm_crtc_helper_atomic_check,
I think you could have an .mode_valid callback that just checks the fixed mode.
Got it.
+/*
+ * Encoder
+ */
+
+static const struct drm_encoder_funcs st7571_encoder_funcs = {
+ .destroy = drm_encoder_cleanup,
+};
I recommend to have an encoder .atomic_{en,dis}able callbacks to init and turn
off your display respectively. That way, the driver can call st7571_lcd_init()
only when the display is going to be used instead of at probe time.
I will look into this as well.
...
+static enum drm_mode_status st7571_mode_config_mode_valid(struct drm_device *dev,
+ const struct drm_display_mode *mode)
+{
+ struct st7571_device *st7571 = drm_to_st7571(dev);
+
+ return drm_crtc_helper_mode_valid_fixed(&st7571->crtc, mode, &st7571->mode);
+}
The fact that you are calling a drm_crtc_helper here is an indication that probably
this should be done in a struct drm_crtc_helper_funcs .mode_valid callback instead,
as mentioned above.
I will move it to drm_crtc_helper_funcs.
+
+static const struct drm_mode_config_funcs st7571_mode_config_funcs = {
+ .fb_create = drm_gem_fb_create_with_dirty,
+ .mode_valid = st7571_mode_config_mode_valid,
And that way you could just drop this handler.
Yep, thanks.
+ .atomic_check = drm_atomic_helper_check,
+ .atomic_commit = drm_atomic_helper_commit,
+};
+
...
+static int st7571_probe(struct i2c_client *client)
+{
+ struct st7571_device *st7571;
+ struct drm_device *dev;
+ int ret;
+
+ st7571 = devm_drm_dev_alloc(&client->dev, &st7571_driver,
+ struct st7571_device, dev);
+ if (IS_ERR(st7571))
+ return PTR_ERR(st7571);
+
+ dev = &st7571->dev;
+ st7571->client = client;
+ i2c_set_clientdata(client, st7571);
+
+ ret = st7571_parse_dt(st7571);
+ if (ret)
+ return ret;
+
+ st7571->mode = st7571_mode(st7571);
+
+ /*
+ * The chip nacks some messages but still works as expected.
+ * If the adapter does not support protocol mangling do
+ * not set the I2C_M_IGNORE_NAK flag at the expense * of possible
+ * cruft in the logs.
+ */
+ if (i2c_check_functionality(client->adapter, I2C_FUNC_PROTOCOL_MANGLING))
+ st7571->ignore_nak = true;
+
+ st7571->regmap = devm_regmap_init(&client->dev, &st7571_regmap_bus,
+ client, &st7571_regmap_config);
+ if (IS_ERR(st7571->regmap)) {
+ dev_err(&client->dev, "Failed to initialize regmap\n");
If you use dev_err_probe(), you can give some indication to users about
what failed. It prints messages in the /sys/kernel/debug/devices_deferred
debugfs entry.
Got it, thanks.
+
+static void st7571_remove(struct i2c_client *client)
+{
+ struct st7571_device *st7571 = i2c_get_clientdata(client);
+
+ drm_dev_unplug(&st7571->dev);
I think you are missing a drm_atomic_helper_shutdown() here.
This is a change for v3. As the device has been unplugged already, it
won't do anything, so I removed it.
Isn't it right to do so?
And also a struct i2c_driver .shutdown callback to call to
drm_atomic_helper_shutdown() as well.
--
Best regards,
Javier Martinez Canillas
Core Platforms
Red Hat
Best regards,
Marcus Folkesson
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)