Re: [PATCH] drm/i915/bxt: Fix wrongly placed ')' in I915_READ()

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 14 Oct 2015, Dave Gordon <david.s.gordon@intel.com> wrote:
> On 17/09/15 14:20, Damien Lespiau wrote:
>> Not the first time! not the last time?
>>
>> There is a possibility to use gcc 5's -Wbool-compare to try and compare
>> (reg) in those macros to a constant and gcc will warn that the
>> comparison between a boolean expression and a constant is always either
>> true or false. Maybe.
>
> Since boolean true (1) cannot be a valid argument to this macro, it 
> could contain a compile-time check that the parameter is not 1; if 
> boolean false (0) happens not to be a valid register address (BSpec says 
> MMIO 0 is reserved) the macro could check that the argument is neither 
> of these values, and the compiler might then detect that all possible 
> paths lead to a compile-time error. Something like this?

The past errors have also been of the form

	if (I915_READ(SOME_REG(pipe) & MASK) == val)

which isn't caught by your check. See [1].


BR,
Jani.


[1] http://mid.gmane.org/1442595836-23981-1-git-send-email-ville.syrjala@linux.intel.com





>
> #define I915_READ(reg)                                                 \
>          ({                                                             \
>              if (__builtin_constant_p(reg)) {                           \
>                  BUILD_BUG_ON((reg) == false);                          \
>                  BUILD_BUG_ON((reg) == true);                           \
>              }                                                          \
>              dev_priv->uncore.funcs.mmio_readl(dev_priv, (reg), true);  \
>          })
>
> Interestingly, that reported three errors, all in intel_dsi.c where the 
> port-selection macros use 0s to fill in dummy elements when less than 3 
> ports are being used.
>
> In function ‘intel_dsi_get_hw_state’
> In function ‘intel_dsi_port_disable’
> In function ‘intel_dsi_port_enable’
>
> Other than that, there weren't any cases where a bool constant was being 
> passed to this specific macro (as of today).
>
> .Dave.
>
>> Cc: Imre Deak <imre.deak@intel.com>
>> Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
>> ---
>>   drivers/gpu/drm/i915/intel_ddi.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
>> index 4823184..5b600bf 100644
>> --- a/drivers/gpu/drm/i915/intel_ddi.c
>> +++ b/drivers/gpu/drm/i915/intel_ddi.c
>> @@ -2882,7 +2882,7 @@ static bool bxt_ddi_pll_get_hw_state(struct drm_i915_private *dev_priv,
>>   	 * here just read out lanes 0/1 and output a note if lanes 2/3 differ.
>>   	 */
>>   	hw_state->pcsdw12 = I915_READ(BXT_PORT_PCS_DW12_LN01(port));
>> -	if (I915_READ(BXT_PORT_PCS_DW12_LN23(port) != hw_state->pcsdw12))
>> +	if (I915_READ(BXT_PORT_PCS_DW12_LN23(port)) != hw_state->pcsdw12)
>>   		DRM_DEBUG_DRIVER("lane stagger config different for lane 01 (%08x) and 23 (%08x)\n",
>>   				 hw_state->pcsdw12,
>>   				 I915_READ(BXT_PORT_PCS_DW12_LN23(port)));
>
>
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-- 
Jani Nikula, Intel Open Source Technology Center
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