Re: [PATCH 1/1] drm/i915/dsi: silence a warning about uninitialized return value

Hello,

I sent the patch below a few weeks ago. I got some comments (cf. [1]) which looked good, but the patch has not been merged in linux-next yet. Do I need to fix something (like rewrite the commit message) in order to get it merged?

Thanks, Nicolas

[1] https://patchwork.freedesktop.org/patch/108941/

On 04/09/16 20:58, Nicolas Iooss wrote:

When building the kernel with clang and some warning flags, the compiler reports that the return value of dcs_get_backlight() may be uninitialized:

drivers/gpu/drm/i915/intel_dsi_dcs_backlight.c:53:2: error: variable
'data' is used uninitialized whenever 'for' loop exits because its
condition is false [-Werror,-Wsometimes-uninitialized]
        for_each_dsi_port(port, intel_dsi->dcs_backlight_ports) {
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/i915/intel_dsi.h:126:49: note: expanded from macro
'for_each_dsi_port'
#define for_each_dsi_port(__port, __ports_mask)
                            for_each_port_masked(__port, __ports_mask)
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/i915/i915_drv.h:322:26: note: expanded from macro
'for_each_port_masked'
    for ((__port) = PORT_A; (__port) < I915_MAX_PORTS; (__port)++)  \
                            ^~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/i915/intel_dsi_dcs_backlight.c:60:9: note:
uninitialized use occurs here
        return data;
               ^~~~

As intel_dsi->dcs_backlight_ports seems to be always initialized to a non-null value, the content of the for loop is always executed and there is no bug in the current code. Nevertheless the compiler has no way of knowing that assumption, so initialize variable 'data' to silence the warning here.

Signed-off-by: Nicolas Iooss nicolas.iooss_linux@m4x.org

drivers/gpu/drm/i915/intel_dsi_dcs_backlight.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dsi_dcs_backlight.c b/drivers/gpu/drm/i915/intel_dsi_dcs_backlight.c index ac7c6020c443..eec45856f910 100644 --- a/drivers/gpu/drm/i915/intel_dsi_dcs_backlight.c +++ b/drivers/gpu/drm/i915/intel_dsi_dcs_backlight.c @@ -46,7 +46,7 @@ static u32 dcs_get_backlight(struct intel_connector *connector) struct intel_encoder *encoder = connector->encoder; struct intel_dsi *intel_dsi = enc_to_intel_dsi(&encoder->base); struct mipi_dsi_device *dsi_device;

• u8 data;

• u8 data = 0; enum port port;

  /* FIXME: Need to take care of 16 bit brightness level */