Re: [PATCH 1/4] drm/i915/display: Limit max joined dotclock on joiner pipes available

On Mon, 10 Aug 2026, "Nautiyal, Ankit K" <[email protected]> wrote:
> On 8/7/2026 6:04 PM, Jani Nikula wrote:
>> Multiplying the max dotclock based on joiner availability on the
>> platform alone does not take into account the actual pipes (possibly
>> with some fused) available for joining.
>>
>> Limit the max joined dotclock based on the actual pipes available for
>> joining. Add helpers for figuring out the valid primary pipes, based on
>> having the required joiners and amount of consecutive pipes available.
>>
>> v2: Check for consecutive pipes available (Ankit)
>>
>> Cc: Ankit Nautiyal <[email protected]>
>> Signed-off-by: Jani Nikula <[email protected]>
>> ---
>>   drivers/gpu/drm/i915/display/intel_display.c | 51 +++++++++++++++++++-
>>   drivers/gpu/drm/i915/display/intel_display.h |  1 +
>>   2 files changed, 50 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
>> index 829d7a411dcc..c958b2a92cc7 100644
>> --- a/drivers/gpu/drm/i915/display/intel_display.c
>> +++ b/drivers/gpu/drm/i915/display/intel_display.c
>> @@ -193,6 +193,53 @@ is_trans_port_sync_mode(const struct intel_crtc_state *crtc_state)
>>   		is_trans_port_sync_slave(crtc_state);
>>   }
>>   
>> +/*
>> + * Return a bitmask of all the start indices of consecutive bitfields of size
>> + * width in mask.
>> + */
>> +static unsigned long find_consecutive_bits(unsigned long mask, int width)
>> +{
>> +	unsigned long bit, out_mask = 0;
>> +
>> +	if (!width)
>> +		return 0;
>> +
>> +	for_each_set_bit(bit, &mask, BITS_PER_TYPE(mask)) {
>> +		/* For each set bit, see if the following bits are set also */
>> +		unsigned long bitfield = GENMASK(bit + width - 1, bit);
>> +
>> +		if ((mask & bitfield) == bitfield)
>> +			out_mask |= BIT(bit);
>> +	}
>> +
>> +	return out_mask;
>
> This is very clever!
>
> This fits very nicely with the part where we want to check if joiner is 
> supported "for a specific crtc" during compute_config phase.

Yay, thanks!

> This works even for width = 1 as well, but it's better to handle the 
> case separately as you have already done, it's intuitive and avoids 
> iterating through the bits.
>
> Reviewed-by: Ankit Nautiyal <[email protected]>

Thanks for the review, pushed the lot to din.

BR,
Jani.

>
>
>> +}
>> +
>> +/*
>> + * Return a bitmask of all valid joiner primary pipes for joining
>> + * num_joined_pipes pipes. For completeness, return all valid pipes for
>> + * num_joined_pipes == 1.
>> + *
>> + * Return 0 if the platform doesn't support joining for the requested number of
>> + * pipes, or there are not enough consecutive pipes available.
>> + */
>> +u8 intel_joiner_valid_primary_pipe_mask(struct intel_display *display, int num_joined_pipes)
>> +{
>> +	if (num_joined_pipes == 1) {
>> +		return DISPLAY_RUNTIME_INFO(display)->pipe_mask;
>> +	} else if (num_joined_pipes == 2) {
>> +		if (!HAS_UNCOMPRESSED_JOINER(display) && !HAS_BIGJOINER(display))
>> +			return 0;
>> +	} else if (num_joined_pipes == 4) {
>> +		if (!HAS_ULTRAJOINER(display))
>> +			return 0;
>> +	} else {
>> +		return 0;
>> +	}
>> +
>> +	return find_consecutive_bits(DISPLAY_RUNTIME_INFO(display)->pipe_mask, num_joined_pipes);
>> +}
>> +
>>   static enum pipe joiner_primary_pipe(const struct intel_crtc_state *crtc_state)
>>   {
>>   	return ffs(crtc_state->joiner_pipes) - 1;
>> @@ -8113,9 +8160,9 @@ static int max_dotclock(struct intel_display *display)
>>   {
>>   	int max_dotclock = display->cdclk.max_dotclk_freq;
>>   
>> -	if (HAS_ULTRAJOINER(display))
>> +	if (intel_joiner_valid_primary_pipe_mask(display, 4))
>>   		max_dotclock *= 4;
>> -	else if (HAS_UNCOMPRESSED_JOINER(display) || HAS_BIGJOINER(display))
>> +	else if (intel_joiner_valid_primary_pipe_mask(display, 2))
>>   		max_dotclock *= 2;
>>   
>>   	return max_dotclock;
>> diff --git a/drivers/gpu/drm/i915/display/intel_display.h b/drivers/gpu/drm/i915/display/intel_display.h
>> index 57ea4f2edf2a..e7ecae9d2d21 100644
>> --- a/drivers/gpu/drm/i915/display/intel_display.h
>> +++ b/drivers/gpu/drm/i915/display/intel_display.h
>> @@ -373,6 +373,7 @@ intel_cpu_transcoder_mode_valid(struct intel_display *display,
>>   enum phy intel_port_to_phy(struct intel_display *display, enum port port);
>>   bool is_trans_port_sync_mode(const struct intel_crtc_state *state);
>>   bool is_trans_port_sync_master(const struct intel_crtc_state *state);
>> +u8 intel_joiner_valid_primary_pipe_mask(struct intel_display *display, int num_joined_pipes);
>>   u8 intel_crtc_joined_pipe_mask(const struct intel_crtc_state *crtc_state);
>>   bool intel_crtc_is_joiner_secondary(const struct intel_crtc_state *crtc_state);
>>   bool intel_crtc_is_joiner_primary(const struct intel_crtc_state *crtc_state);

-- 
Jani Nikula, Intel