Re: [PATCH linux-next] drm/i915/display: Remove unused variable and its assignment.

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Oct 18, 2021 at 08:43:31AM +0000, luo penghao wrote:
> Variable is not used in functions, and its assignment is redundant too.
> So it should be deleted.
> 
> The clang_analyzer complains as follows:
> 
> drivers/gpu/drm/i915/display/intel_dpll.c:1653:2 warning:
> Value stored to 'bestm1' is never read.
> 
> drivers/gpu/drm/i915/display/intel_dpll.c:1651:2 warning:
> Value stored to 'bestn' is never read.
> 
> Reported-by: Zeal Robot <zealci@zte.com.cn>
> Signed-off-by: luo penghao <luo.penghao@zte.com.cn>
> ---
>  drivers/gpu/drm/i915/display/intel_dpll.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dpll.c b/drivers/gpu/drm/i915/display/intel_dpll.c
> index b84ed4a..28b1616 100644
> --- a/drivers/gpu/drm/i915/display/intel_dpll.c
> +++ b/drivers/gpu/drm/i915/display/intel_dpll.c
> @@ -1644,13 +1644,11 @@ static void chv_prepare_pll(const struct intel_crtc_state *crtc_state)
>  	enum pipe pipe = crtc->pipe;
>  	enum dpio_channel port = vlv_pipe_to_channel(pipe);
>  	u32 loopfilter, tribuf_calcntr;
> -	u32 bestn, bestm1, bestm2, bestp1, bestp2, bestm2_frac;
> +	u32 bestm2, bestp1, bestp2, bestm2_frac;
>  	u32 dpio_val;
>  	int vco;
>  
> -	bestn = crtc_state->dpll.n;

This one we could use. For some reason we hardcode it to
1 now, which is correct for our use cases but I don't really
see a reason to hardcode it here. We are supposed to calculate
it correctly after all, and chv_crtc_clock_get() also just blindly
reads it out.

>  	bestm2_frac = crtc_state->dpll.m2 & 0x3fffff;
> -	bestm1 = crtc_state->dpll.m1;

This one is a bit trickier since I don't think the spec even
gives us other values. But we could assert that it's correct.

Some something along these lines I think would be best:
+ drm_WARN_ON(&dev_priv->drm, bestm1 != 2);
  vlv_dpio_write(dev_priv, pipe, CHV_PLL_DW1(port),
                 DPIO_CHV_M1_DIV_BY_2 |
- 		 1 << DPIO_CHV_N_DIV_SHIFT);
+ 		 bestn << DPIO_CHV_N_DIV_SHIFT);

-- 
Ville Syrjälä
Intel