diff options
Diffstat (limited to 'drivers/gpu/drm/i915/intel_display.c')
| -rw-r--r-- | drivers/gpu/drm/i915/intel_display.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index 20fb8dd13184..654b8a0c28ee 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -6290,6 +6290,17 @@ intel_reduce_m_n_ratio(uint32_t *num, uint32_t *den) static void compute_m_n(unsigned int m, unsigned int n, uint32_t *ret_m, uint32_t *ret_n) { + /* + * Reduce M/N as much as possible without loss in precision. Several DP + * dongles in particular seem to be fussy about too large *link* M/N + * values. The passed in values are more likely to have the least + * significant bits zero than M after rounding below, so do this first. + */ + while ((m & 1) == 0 && (n & 1) == 0) { + m >>= 1; + n >>= 1; + } + *ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX); *ret_m = div_u64((uint64_t) m * *ret_n, n); intel_reduce_m_n_ratio(ret_m, ret_n); |