Re: [PATCH v2 01/12] drm/i915: Fix sha_text population code

[Ramalingam C <ramalingam.c@intel.com>]

On 2019-12-12 at 14:02:19 -0500, Sean Paul wrote:
> From: Sean Paul <seanpaul@chromium.org>
> 
> This patch fixes a few bugs:
> 
> 1- We weren't taking into account sha_leftovers when adding multiple
>    ksvs to sha_text. As such, we were or'ing the end of ksv[j - 1] with
>    the beginning of ksv[j]
> 
> 2- In the sha_leftovers == 2 and sha_leftovers == 3 case, bstatus was
>    being placed on the wrong half of sha_text, overlapping the leftover
>    ksv value
> 
> 3- In the sha_leftovers == 2 case, we need to manually terminate the
>    byte stream with 0x80 since the hardware doesn't have enough room to
>    add it after writing M0
> 
> The upside is that all of the "HDCP supported" HDMI repeaters I could
> find on Amazon just strip HDCP anyways, so it turns out to be _really_
> hard to hit any of these cases without an MST hub, which is not (yet)
> supported. Oh, and the sha_leftovers == 1 case works perfectly!

Yes. The repeaters tested at our side too with sha_leftovers = 1 with
mostly ksv count of 1. non availability of the repeaters is killer here.
> 
> Fixes: ee5e5e7a5e0f ("drm/i915: Add HDCP framework + base implementation")
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ramalingam C <ramalingam.c@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Sean Paul <seanpaul@chromium.org>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: intel-gfx@lists.freedesktop.org
> Cc: <stable@vger.kernel.org> # v4.17+
> Signed-off-by: Sean Paul <seanpaul@chromium.org>
> Link: https://patchwork.freedesktop.org/patch/msgid/20191203173638.94919-2-sean@poorly.run #v1
> 
> Changes in v2:
> -None
> ---
>  drivers/gpu/drm/i915/display/intel_hdcp.c | 25 +++++++++++++++++------
>  include/drm/drm_hdcp.h                    |  3 +++
>  2 files changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c b/drivers/gpu/drm/i915/display/intel_hdcp.c
> index 0fdbd39f6641..eaab9008feef 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdcp.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
> @@ -335,8 +335,10 @@ int intel_hdcp_validate_v_prime(struct intel_connector *connector,
>  
>  		/* Fill up the empty slots in sha_text and write it out */
>  		sha_empty = sizeof(sha_text) - sha_leftovers;
> -		for (j = 0; j < sha_empty; j++)
> -			sha_text |= ksv[j] << ((sizeof(sha_text) - j - 1) * 8);
> +		for (j = 0; j < sha_empty; j++) {
> +			u8 off = ((sizeof(sha_text) - j - 1 - sha_leftovers) * 8);
Didn't hit this as ksv count was 1 mostly with sha_leftovers = 1.
Thanks for fixing it.
> +			sha_text |= ksv[j] << off;
> +		}
>  
>  		ret = intel_write_sha_text(dev_priv, sha_text);
>  		if (ret < 0)
> @@ -426,7 +428,7 @@ int intel_hdcp_validate_v_prime(struct intel_connector *connector,
>  	} else if (sha_leftovers == 2) {
>  		/* Write 32 bits of text */
>  		I915_WRITE(HDCP_REP_CTL, rep_ctl | HDCP_SHA1_TEXT_32);
> -		sha_text |= bstatus[0] << 24 | bstatus[1] << 16;
> +		sha_text |= bstatus[0] << 8 | bstatus[1];
>  		ret = intel_write_sha_text(dev_priv, sha_text);
>  		if (ret < 0)
>  			return ret;
> @@ -440,16 +442,27 @@ int intel_hdcp_validate_v_prime(struct intel_connector *connector,
>  				return ret;
>  			sha_idx += sizeof(sha_text);
>  		}
> +
> +		/*
> +		 * Terminate the SHA-1 stream by hand. For the other leftover
> +		 * cases this is appended by the hardware.
> +		 */
> +		I915_WRITE(HDCP_REP_CTL, rep_ctl | HDCP_SHA1_TEXT_32);
> +		sha_text = DRM_HDCP_SHA1_TERMINATOR << 24;
> +		ret = intel_write_sha_text(dev_priv, sha_text);
> +		if (ret < 0)
> +			return ret;
> +		sha_idx += sizeof(sha_text);
>  	} else if (sha_leftovers == 3) {
> -		/* Write 32 bits of text */
> +		/* Write 32 bits of text (filled from LSB) */
>  		I915_WRITE(HDCP_REP_CTL, rep_ctl | HDCP_SHA1_TEXT_32);
> -		sha_text |= bstatus[0] << 24;
> +		sha_text |= bstatus[0];

Looks good to me though this path never been exercised. Hopefully MST
will do it.

Reviewed-by: Ramalingam C <ramalingam.c@intel.com>

>  		ret = intel_write_sha_text(dev_priv, sha_text);
>  		if (ret < 0)
>  			return ret;
>  		sha_idx += sizeof(sha_text);
>  
> -		/* Write 8 bits of text, 24 bits of M0 */
> +		/* Write 8 bits of text (filled from LSB), 24 bits of M0 */
>  		I915_WRITE(HDCP_REP_CTL, rep_ctl | HDCP_SHA1_TEXT_8);
>  		ret = intel_write_sha_text(dev_priv, bstatus[1]);
>  		if (ret < 0)
> diff --git a/include/drm/drm_hdcp.h b/include/drm/drm_hdcp.h
> index 06a11202a097..20498c822204 100644
> --- a/include/drm/drm_hdcp.h
> +++ b/include/drm/drm_hdcp.h
> @@ -29,6 +29,9 @@
>  /* Slave address for the HDCP registers in the receiver */
>  #define DRM_HDCP_DDC_ADDR			0x3A
>  
> +/* Value to use at the end of the SHA-1 bytestream used for repeaters */
> +#define DRM_HDCP_SHA1_TERMINATOR		0x80
> +
>  /* HDCP register offsets for HDMI/DVI devices */
>  #define DRM_HDCP_DDC_BKSV			0x00
>  #define DRM_HDCP_DDC_RI_PRIME			0x08
> -- 
> Sean Paul, Software Engineer, Google / Chromium OS
> 
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