On Wed, Mar 22, 2017 at 04:27:36PM -0700, clinton.a.taylor@xxxxxxxxx wrote:
> From: Clint Taylor <clinton.a.taylor@xxxxxxxxx>
>
> Several major vendor USB-C->HDMI converters fail to recover a 5.4 GHz 1 lane
> signal if the Data Link N is greater than 0x80000.
> Patch detects when 1 lane 5.4 GHz signal is being used and makes the maximum
> value 20 bit instead of the maximum specification supported 24 bit value.
>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Cc: Anusha Srivatsa <anusha.srivatsa@xxxxxxxxx>
>
> Signed-off-by: Clint Taylor <clinton.a.taylor@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_reg.h | 2 ++
> drivers/gpu/drm/i915/intel_display.c | 15 +++++++++++----
> 2 files changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 04c8f69..838d8d5 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -4869,6 +4869,8 @@ enum {
>
> #define DATA_LINK_M_N_MASK (0xffffff)
> #define DATA_LINK_N_MAX (0x800000)
> +/* Maximum N value useable on some DP->HDMI converters */
> +#define DATA_LINK_REDUCED_N_MAX (0x80000)
>
> #define _PIPEA_DATA_N_G4X 0x70054
> #define _PIPEB_DATA_N_G4X 0x71054
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 010e5dd..6e1fdd2 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -6315,9 +6315,10 @@ static int intel_crtc_compute_config(struct intel_crtc *crtc,
> }
>
> static void compute_m_n(unsigned int m, unsigned int n,
> - uint32_t *ret_m, uint32_t *ret_n)
> + uint32_t *ret_m, uint32_t *ret_n,
> + uint32_t max_link_n)
> {
> - *ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX);
> + *ret_n = min_t(unsigned int, roundup_pow_of_two(n), max_link_n);
> *ret_m = div_u64((uint64_t) m * *ret_n, n);
> intel_reduce_m_n_ratio(ret_m, ret_n);
> }
> @@ -6327,14 +6328,20 @@ static void compute_m_n(unsigned int m, unsigned int n,
> int pixel_clock, int link_clock,
> struct intel_link_m_n *m_n)
> {
> + uint32_t max_link_n = DATA_LINK_N_MAX;
> m_n->tu = 64;
>
> + if ((nlanes==1) && (link_clock >= 540000))
> + max_link_n = DATA_LINK_REDUCED_N_MAX;
> +
Is this very specific to 1 lane 5.4Gbps configuration or you think
this will be needed for higher rates and 1 lane?
If not why dont we make it very specific link_clock ==540000?
Regards
Manasi
> compute_m_n(bits_per_pixel * pixel_clock,
> link_clock * nlanes * 8,
> - &m_n->gmch_m, &m_n->gmch_n);
> + &m_n->gmch_m, &m_n->gmch_n,
> + max_link_n);
>
> compute_m_n(pixel_clock, link_clock,
> - &m_n->link_m, &m_n->link_n);
> + &m_n->link_m, &m_n->link_n,
> + max_link_n);
> }
>
> static inline bool intel_panel_use_ssc(struct drm_i915_private *dev_priv)
> --
> 1.7.9.5
>
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