Re: [Intel-gfx] [PATCH] drm/i915/dsi: fix VBT send packet port selection for ICL+

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, May 20, 2022 at 12:46:00PM +0300, Jani Nikula wrote:
> The VBT send packet port selection was never updated for ICL+ where the
> 2nd link is on port B instead of port C as in VLV+ DSI.
> 
> First, single link DSI needs to use the configured port instead of
> relying on the VBT sequence block port. Remove the hard-coded port C
> check here and make it generic. For reference, see commit f915084edc5a
> ("drm/i915: Changes related to the sequence port no for") for the
> original VLV specific fix.
> 
> Second, the sequence block port number is either 0 or 1, where 1
> indicates the 2nd link. Remove the hard-coded port C here for 2nd
> link. (This could be a "find second set bit" on DSI ports, but just
> check the two possible options.)
> 
> Third, sanity check the result with a warning to avoid a NULL pointer
> dereference.
> 
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5984
> Cc: stable@vger.kernel.org # v4.19+
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dsi_vbt.c | 33 +++++++++++++-------
>  1 file changed, 22 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dsi_vbt.c b/drivers/gpu/drm/i915/display/intel_dsi_vbt.c
> index f370e9c4350d..dd24aef925f2 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsi_vbt.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsi_vbt.c
> @@ -125,9 +125,25 @@ struct i2c_adapter_lookup {
>  #define  ICL_GPIO_DDPA_CTRLCLK_2	8
>  #define  ICL_GPIO_DDPA_CTRLDATA_2	9
>  
> -static enum port intel_dsi_seq_port_to_port(u8 port)
> +static enum port intel_dsi_seq_port_to_port(struct intel_dsi *intel_dsi,
> +					    u8 seq_port)
>  {
> -	return port ? PORT_C : PORT_A;
> +	/*
> +	 * If single link DSI is being used on any port, the VBT sequence block
> +	 * send packet apparently always has 0 for the port. Just use the port
> +	 * we have configured, and ignore the sequence block port.
> +	 */
> +	if (hweight8(intel_dsi->ports) == 1)
> +		return ffs(intel_dsi->ports) - 1;
> +
> +	if (seq_port) {
> +		if (intel_dsi->ports & PORT_B)
> +			return PORT_B;
> +		else if (intel_dsi->ports & PORT_C)
> +			return PORT_C;
> +	}
> +
> +	return PORT_A;

Hmm. I guess a bit more generic way to express that could be
to just pick the Nth set bit from intel_dsi->ports, where N==seq_port.
Assuming seq_port is just an index. But I guess we're not really
expecting to grow more DSI ports any time soon, so this seems
sufficient for the current situation.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  }
>  
>  static const u8 *mipi_exec_send_packet(struct intel_dsi *intel_dsi,
> @@ -149,15 +165,10 @@ static const u8 *mipi_exec_send_packet(struct intel_dsi *intel_dsi,
>  
>  	seq_port = (flags >> MIPI_PORT_SHIFT) & 3;
>  
> -	/* For DSI single link on Port A & C, the seq_port value which is
> -	 * parsed from Sequence Block#53 of VBT has been set to 0
> -	 * Now, read/write of packets for the DSI single link on Port A and
> -	 * Port C will based on the DVO port from VBT block 2.
> -	 */
> -	if (intel_dsi->ports == (1 << PORT_C))
> -		port = PORT_C;
> -	else
> -		port = intel_dsi_seq_port_to_port(seq_port);
> +	port = intel_dsi_seq_port_to_port(intel_dsi, seq_port);
> +
> +	if (drm_WARN_ON(&dev_priv->drm, !intel_dsi->dsi_hosts[port]))
> +		goto out;
>  
>  	dsi_device = intel_dsi->dsi_hosts[port]->device;
>  	if (!dsi_device) {
> -- 
> 2.30.2

-- 
Ville Syrjälä
Intel