Re: [PATCH] leds: multicolor: limit intensity to max_brightness of LED

[Lee Jones <lee@kernel.org>]

On Thu, 05 Mar 2026, Andy Shevchenko wrote:

> On Fri, Jan 23, 2026 at 11:13:24AM +0100, Michael Tretter wrote:
> > According to Documentation/ABI/testing/sysfs-class-led-multicolor, the
> > intensity should not exceed /sys/class/leds/<led>/max_brightness.
> > 
> > The interface doesn't check the values and higher values may lead to
> > unexpected color changes if the brightness is changed.
> > 
> > Clamp the intensity value to max_brightness.
> 
> This also brings a regression if somebody doesn't care about wrapping around.
> It's possible to return an error instead, but still the user space will be
> broken (in some rare weird cases).
> 
> Again, I care even less about this change, but be always careful,
> the main rule in the kernel "We do NOT break user space".

I'm going to remove this patch for now.

/tmp/next/build/drivers/leds/led-class-multicolor.c: In function 'multi_intensity_store':
/tmp/next/build/include/linux/compiler_types.h:706:45: error: call to '__compiletime_assert_434' declared with attribute error: min(intensity_value[i], led_cdev->max_brightness) signedness error
  706 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |                                             ^
/tmp/next/build/include/linux/compiler_types.h:687:25: note: in definition of macro '__compiletime_assert'
  687 |                         prefix ## suffix();                             \
      |                         ^~~~~~
/tmp/next/build/include/linux/compiler_types.h:706:9: note: in expansion of macro '_compiletime_assert'
  706 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |         ^~~~~~~~~~~~~~~~~~~
/tmp/next/build/include/linux/build_bug.h:40:37: note: in expansion of macro 'compiletime_assert'
   40 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
      |                                     ^~~~~~~~~~~~~~~~~~
/tmp/next/build/include/linux/minmax.h:93:9: note: in expansion of macro 'BUILD_BUG_ON_MSG'
   93 |         BUILD_BUG_ON_MSG(!__types_ok(ux, uy),           \
      |         ^~~~~~~~~~~~~~~~
/tmp/next/build/include/linux/minmax.h:98:9: note: in expansion of macro '__careful_cmp_once'
   98 |         __careful_cmp_once(op, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
      |         ^~~~~~~~~~~~~~~~~~
/tmp/next/build/include/linux/minmax.h:105:25: note: in expansion of macro '__careful_cmp'
  105 | #define min(x, y)       __careful_cmp(min, x, y)
      |                         ^~~~~~~~~~~~~
/tmp/next/build/drivers/leds/led-class-multicolor.c:51:38: note: in expansion of macro 'min'
   51 |                 intensity_value[i] = min(intensity_value[i],
      |               

-- 
Lee Jones [李琼斯]