Re: [Intel-gfx] [PATCH 15/26] drm/i915: Make M/N checks non-fuzzy

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

On Tue, 03 May 2022, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Now that we no longer fuzz M/N during fastset these should
> match exctly.
>
> TODO: we may need to do something for fastboot here as the
> VBIOS/GOP may not compute M/N exactly the same way we do.
> Though I guess we could try to match the VBIOS/GOP exactly.

I see that later patches change the M/N calculation, and that may be
enough.

But if GOP isn't consistent about this (I don't know), it's going to be
whack-a-mole if we get regression reports on not having fastboot.

Mmh. If we support seamless M/N change, could we do that on fastboot?

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 49 ++++----------------
>  1 file changed, 8 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 86971be92e57..198c6340a463 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -5832,47 +5832,15 @@ bool intel_fuzzy_clock_check(int clock1, int clock2)
>  	return false;
>  }
>  
> -static bool
> -intel_compare_m_n(unsigned int m, unsigned int n,
> -		  unsigned int m2, unsigned int n2,
> -		  bool exact)
> -{
> -	if (m == m2 && n == n2)
> -		return true;
> -
> -	if (exact || !m || !n || !m2 || !n2)
> -		return false;
> -
> -	BUILD_BUG_ON(DATA_LINK_M_N_MASK > INT_MAX);
> -
> -	if (n > n2) {
> -		while (n > n2) {
> -			m2 <<= 1;
> -			n2 <<= 1;
> -		}
> -	} else if (n < n2) {
> -		while (n < n2) {
> -			m <<= 1;
> -			n <<= 1;
> -		}
> -	}
> -
> -	if (n != n2)
> -		return false;
> -
> -	return intel_fuzzy_clock_check(m, m2);
> -}
> -
>  static bool
>  intel_compare_link_m_n(const struct intel_link_m_n *m_n,
> -		       const struct intel_link_m_n *m2_n2,
> -		       bool exact)
> +		       const struct intel_link_m_n *m2_n2)
>  {
>  	return m_n->tu == m2_n2->tu &&
> -		intel_compare_m_n(m_n->data_m, m_n->data_n,
> -				  m2_n2->data_m, m2_n2->data_n, exact) &&
> -		intel_compare_m_n(m_n->link_m, m_n->link_n,
> -				  m2_n2->link_m, m2_n2->link_n, exact);
> +		m_n->data_m == m2_n2->data_m &&
> +		m_n->data_n == m2_n2->data_n &&
> +		m_n->link_m == m2_n2->link_m &&
> +		m_n->link_n == m2_n2->link_n;
>  }
>  
>  static bool
> @@ -6066,8 +6034,7 @@ intel_pipe_config_compare(const struct intel_crtc_state *current_config,
>  
>  #define PIPE_CONF_CHECK_M_N(name) do { \
>  	if (!intel_compare_link_m_n(&current_config->name, \
> -				    &pipe_config->name,\
> -				    !fastset)) { \
> +				    &pipe_config->name)) { \
>  		pipe_config_mismatch(fastset, crtc, __stringify(name), \
>  				     "(expected tu %i data %i/%i link %i/%i, " \
>  				     "found tu %i, data %i/%i link %i/%i)", \
> @@ -6114,9 +6081,9 @@ intel_pipe_config_compare(const struct intel_crtc_state *current_config,
>   */
>  #define PIPE_CONF_CHECK_M_N_ALT(name, alt_name) do { \
>  	if (!intel_compare_link_m_n(&current_config->name, \
> -				    &pipe_config->name, !fastset) && \
> +				    &pipe_config->name) && \
>  	    !intel_compare_link_m_n(&current_config->alt_name, \
> -				    &pipe_config->name, !fastset)) { \
> +				    &pipe_config->name)) { \
>  		pipe_config_mismatch(fastset, crtc, __stringify(name), \
>  				     "(expected tu %i data %i/%i link %i/%i, " \
>  				     "or tu %i data %i/%i link %i/%i, " \

-- 
Jani Nikula, Intel Open Source Graphics Center