Re: [PATCH v2 1/2] drm: Add support for DP 1.4 Compliance edid corruption test 4.2.2.6

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

On Fri, 01 Nov 2019, "Jerry (Fangzhi) Zuo" <Jerry.Zuo@amd.com> wrote:
> DP 1.4 edid corruption test requires source DUT to write calculated
> CRC, not the corrupted CRC from reference sink.
>
> Return the calculated CRC back, and initiate the required sequence.
>
> -v2: Have separate routine for returning real CRC
>
> Signed-off-by: Jerry (Fangzhi) Zuo <Jerry.Zuo@amd.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 36 ++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_edid.c      | 14 ++++++++++++++
>  include/drm/drm_connector.h     |  7 +++++++
>  include/drm/drm_dp_helper.h     |  3 +++
>  4 files changed, 60 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index ffc68d305afe..75dbd30c62a7 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -336,6 +336,42 @@ int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
>  }
>  EXPORT_SYMBOL(drm_dp_dpcd_read_link_status);
>  
> +/**
> +  * drm_dp_send_bad_edid_checksum() - send back real edid checksum value
> +  * @aux: DisplayPort AUX channel
> +  * @bad_edid_checksum: real edid checksum for the last block
> +  *
> +  * Returns true on success
> +  */
> +bool drm_dp_send_bad_edid_checksum(struct drm_dp_aux *aux,
> +                                u8 bad_edid_checksum)
> +{
> +        u8 link_edid_read = 0, auto_test_req = 0;
> +        u8 test_resp = 0;
> +
> +        drm_dp_dpcd_read(aux, DP_DEVICE_SERVICE_IRQ_VECTOR, &auto_test_req, 1);
> +        auto_test_req &= DP_AUTOMATED_TEST_REQUEST;
> +
> +        drm_dp_dpcd_read(aux, DP_TEST_REQUEST, &link_edid_read, 1);
> +        link_edid_read &= DP_TEST_LINK_EDID_READ;
> +
> +        if (!auto_test_req || !link_edid_read) {
> +                DRM_DEBUG_KMS("Source DUT does not support TEST_EDID_READ\n");
> +                return false;
> +        }
> +
> +        drm_dp_dpcd_write(aux, DP_DEVICE_SERVICE_IRQ_VECTOR, &auto_test_req, 1);
> +
> +        /* send back checksum for the last edid extension block data */
> +        drm_dp_dpcd_write(aux, DP_TEST_EDID_CHECKSUM, &bad_edid_checksum, 1);
> +
> +        test_resp |= DP_TEST_EDID_CHECKSUM_WRITE;
> +        drm_dp_dpcd_write(aux, DP_TEST_RESPONSE, &test_resp, 1);
> +
> +        return true;
> +}
> +EXPORT_SYMBOL(drm_dp_send_bad_edid_checksum);
> +
>  /**
>   * drm_dp_link_probe() - probe a DisplayPort link for capabilities
>   * @aux: DisplayPort AUX channel
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 82a4ceed3fcf..0598314e3f46 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -1354,6 +1354,17 @@ static int drm_edid_block_checksum(const u8 *raw_edid)
>  	return csum;
>  }
>  
> +static int drm_edid_block_real_checksum(const u8 *raw_edid)
> +{
> +	int i;
> +	u8 csum = 0;
> +
> +	for (i = 0; i < EDID_LENGTH - 1; i++)
> +		csum += raw_edid[i];
> +
> +	return (0x100 - csum);

Now you have two functions that have the loop to calculate checksums,
which is not at all what I tried to tell you to do.

I tried to suggest something like this:

static int drm_edid_block_checksum(const u8 *raw_edid)
{
	int i;
	u8 csum = 0;
	for (i = 0; i < EDID_LENGTH - 1; i++)
		csum += raw_edid[i];

	return 0x100 - csum;
}

static int drm_edid_block_checksum_diff(const u8 *raw_edid)
{
        u8 csum = drm_edid_block_checksum(raw_edid) + raw_edid[EDID_LENGTH - 1];

        return csum;
}

Alternatively, you could have just the function to calculate the
checksum, and then the check is comparing the calculated checksum
against the checksum in the EDID.

BR,
Jani.




> +}
> +
>  static bool drm_edid_is_zero(const u8 *in_edid, int length)
>  {
>  	if (memchr_inv(in_edid, 0, length))
> @@ -1572,6 +1583,9 @@ static void connector_bad_edid(struct drm_connector *connector,
>  			       prefix, DUMP_PREFIX_NONE, 16, 1,
>  			       block, EDID_LENGTH, false);
>  	}
> +
> +	/* Calculate real checksum for the last edid extension block data */
> +	connector->bad_edid_checksum = drm_edid_block_real_checksum(edid + edid[0x7e] * EDID_LENGTH);
>  }
>  
>  /* Get override or firmware EDID */
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 681cb590f952..8442461542b9 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -1345,6 +1345,13 @@ struct drm_connector {
>  	 * rev1.1 4.2.2.6
>  	 */
>  	bool edid_corrupt;
> +	/**
> +         * @bad_edid_checksum: real edid checksum value for corrupted edid block.
> +         * Required in Displayport 1.4 compliance testing
> +         * rev1.1 4.2.2.6
> +         */
> +        uint8_t bad_edid_checksum;
> +
>  
>  	/** @debugfs_entry: debugfs directory for this connector */
>  	struct dentry *debugfs_entry;
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 5a795075d5da..2a7e54bebb18 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -1383,6 +1383,9 @@ static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux,
>  int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
>  				 u8 status[DP_LINK_STATUS_SIZE]);
>  
> +bool drm_dp_send_bad_edid_checksum(struct drm_dp_aux *aux,
> +				u8 bad_edid_checksum);
> +
>  /*
>   * DisplayPort link
>   */

-- 
Jani Nikula, Intel Open Source Graphics Center
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