Re: [PATCH] drm/i915/hdcp: Retry first read and writes to downstream

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

On Wed, 25 Sep 2024, Suraj Kandpal <suraj.kandpal@intel.com> wrote:
> Retry the first read and write to downstream at least 10 times
> with a 50ms delay if not hdcp2 capable. The reason being that

What are the 10 times and 50 ms delay based on?

> during suspend resume Dock usually keep the HDCP2 registers inaccesible
> causing AUX error. This wouldn't be a big problem if the userspace
> just kept retrying with some delay while it continues to play low
> values content but most userpace applications end up throwing an error
> when it receives one from KMD. This makes sure we give the dock
> and the sink devices to complete its power cycle and then try HDCP
> authentication.
>
> Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_hdcp.c | 26 +++++++++++++++++------
>  1 file changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c b/drivers/gpu/drm/i915/display/intel_hdcp.c
> index 2afa92321b08..5f2383c219e8 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdcp.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
> @@ -1512,7 +1512,7 @@ static int hdcp2_authentication_key_exchange(struct intel_connector *connector)
>  	} msgs;
>  	const struct intel_hdcp_shim *shim = hdcp->shim;
>  	size_t size;
> -	int ret;
> +	int ret, i;
>  
>  	/* Init for seq_num */
>  	hdcp->seq_num_v = 0;
> @@ -1522,13 +1522,25 @@ static int hdcp2_authentication_key_exchange(struct intel_connector *connector)
>  	if (ret < 0)
>  		return ret;
>  
> -	ret = shim->write_2_2_msg(connector, &msgs.ake_init,
> -				  sizeof(msgs.ake_init));
> -	if (ret < 0)
> -		return ret;
> +	for (i = 0; i <= 10; i++) {

I'm pretty nitpicky about this. Please avoid <= in the for loop if you
can. Just make it the obvious (i = 0; i < 10; i++), or if you have 1 try
+ 10 retries, then i < 10 + 1 or i < 11.

If the 10 retries is just made up, then maybe just try 10 times total.

> +		if (!intel_hdcp2_get_capability(connector)) {
> +			msleep(50);
> +			continue;
> +		}

This changes behaviour for the first try too. Is that intentional? No
mention in the commit message?

> +
> +		ret = shim->write_2_2_msg(connector, &msgs.ake_init,
> +					  sizeof(msgs.ake_init));
> +		if (ret < 0)
> +			continue;
> +
> +		ret = shim->read_2_2_msg(connector, HDCP_2_2_AKE_SEND_CERT,
> +					 &msgs.send_cert, sizeof(msgs.send_cert));
> +		if (ret < 0)
> +			continue;
> +		else

The else is redundant here.

> +			break;
> +	}
>  
> -	ret = shim->read_2_2_msg(connector, HDCP_2_2_AKE_SEND_CERT,
> -				 &msgs.send_cert, sizeof(msgs.send_cert));
>  	if (ret < 0)
>  		return ret;

-- 
Jani Nikula, Intel