On Wed, Jan 06, 2016 at 01:54:43PM +0100, Maarten Lankhorst wrote:
> This prevents a unnecessary modeset on a dell XPS 13 (2016).
>
> N is always a power of 2, which means that for fuzzy matching we should
> compare for inequality on the n values, then do fuzzy matching on the m
> values.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Tested-by:
Wasn't sure about overflow risks, but as long as the value we compute
originally computed didn't overflow this should be safe.
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> --
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 7afbdc45a278..aa4f1e69b92e 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -12638,19 +12638,22 @@ intel_compare_m_n(unsigned int m, unsigned int n,
>
> BUILD_BUG_ON(DATA_LINK_M_N_MASK > INT_MAX);
>
> - if (m > m2) {
> - while (m > m2) {
> + if (n > n2) {
> + while (n > n2) {
> m2 <<= 1;
> n2 <<= 1;
> }
> - } else if (m < m2) {
> - while (m < m2) {
> + } else if (n < n2) {
> + while (n < n2) {
> m <<= 1;
> n <<= 1;
> }
> }
>
> - return m == m2 && n == n2;
> + if (n != n2)
> + return false;
> +
> + return intel_fuzzy_clock_check(m, m2);
> }
>
> static bool
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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