Re: [PATCH 1/3] fbdev: Fix recursive dependencies wrt BACKLIGHT_CLASS_DEVICE

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On 12/11/24 00:53, Helge Deller wrote:
On 12/11/24 00:37, Helge Deller wrote:
On 12/10/24 16:41, Thomas Zimmermann wrote:
Hi


Am 10.12.24 um 15:34 schrieb Helge Deller:
On 12/10/24 15:29, Helge Deller wrote:
On 12/10/24 15:09, Thomas Zimmermann wrote:
diff --git a/drivers/staging/fbtft/Kconfig b/drivers/staging/fbtft/Kconfig
index 77ab44362f16..577e91ff7bf6 100644
--- a/drivers/staging/fbtft/Kconfig
+++ b/drivers/staging/fbtft/Kconfig
@@ -3,6 +3,7 @@ menuconfig FB_TFT
      tristate "Support for small TFT LCD display modules"
      depends on FB && SPI
      depends on FB_DEVICE
+    depends on BACKLIGHT_DEVICE_CLASS

Typo. Should be BACKLIGHT_CLASS_DEVICE...

Ah, thanks. I'll better check the rest of the series for similar mistakes.


Beside the typo:
In this case, doesn't it make sense to "select BACKLIGHT_DEVICE_CLASS" instead?

That causes the dependency error mentioned in the commit message. This time it's just for fbtft instead of shmobilefb.

If people want the fbtft, backlight support should be enabled too.

As a user-visible option, it should not be auto-selected
unnecessarily.

Right, it should not be auto-selected.
Unless if fbtft really needs it enabled to function.
IMHO all fb/drm drivers have higher priority than some low-level
background backlight controller code.

The DRM panel drivers already depend on the backlight
instead of selecting it. It's the correct approach.

Sounds wrong IMHO.

As I mentioned
in the cover letter, the few remaining driver that select it should
probably be updated.

That dependency sounds weird, but maybe I simply misunderstand your logic...?

As a Linux end user I usually know which graphic cards are in my machine
and which ones I want to enable.
But as a normal user I think I shouldn't be expected to know
that I first need to enable the "backlight class device"
so that I'm then able to afterwards enable the fbtft (or any other drm/fb driver).

Am I wrong?

Looking closer on this...
You propose:

--- a/drivers/staging/fbtft/Kconfig
+++ b/drivers/staging/fbtft/Kconfig
@@ -3,6 +3,7 @@ menuconfig FB_TFT
      tristate "Support for small TFT LCD display modules"
      depends on FB && SPI
      depends on FB_DEVICE
+    depends on BACKLIGHT_DEVICE_CLASS
      depends on GPIOLIB || COMPILE_TEST
      select FB_BACKLIGHT

So, it will depend on BACKLIGHT_DEVICE_CLASS.
But there is "select FB_BACKLIGHT" as well, which is:
config FB_BACKLIGHT
         tristate
         depends on FB
         select BACKLIGHT_CLASS_DEVICE

So, you end up with selecting and depending on BACKLIGHT_CLASS_DEVICE ?

Ok. Ignore this ^^^ . I now understand your cover letter.

Looking at your DRM tiny drivers and the i915/gma500 DRM drivers,
there is a "select BACKLIGHT_CLASS_DEVICE" in those.

So, isn't the right approach then something like:

--- a/drivers/staging/fbtft/Kconfig
       tristate "Support for small TFT LCD display modules"
       depends on FB && SPI
       depends on FB_DEVICE
  +    select BACKLIGHT_DEVICE_CLASS
       depends on GPIOLIB || COMPILE_TEST
       select FB_BACKLIGHT

config FB_BACKLIGHT
          tristate
          depends on FB
  +       depends on BACKLIGHT_CLASS_DEVICE

?




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