Re: [Freedreno] [PATCH v2 13/13] drm/msm: Implement HDCP 1.x using the new drm HDCP helpers

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On 2021-09-28 11:02, Sean Paul wrote:
On Tue, Sep 21, 2021 at 07:25:41PM -0700, abhinavk@xxxxxxxxxxxxxx wrote:
On 2021-09-15 13:38, Sean Paul wrote:
> From: Sean Paul <seanpaul@xxxxxxxxxxxx>
>
> This patch adds HDCP 1.x support to msm DP connectors using the new HDCP
> helpers.
>
> Cc: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> Signed-off-by: Sean Paul <seanpaul@xxxxxxxxxxxx>
> Link:
> https://patchwork.freedesktop.org/patch/msgid/20210913175747.47456-15-sean@xxxxxxxxxx
> #v1
>
> Changes in v2:
> -Squash [1] into this patch with the following changes (Stephen)
>   -Update the sc7180 dtsi file
>   -Remove resource names and just use index (Stephen)
>


> [1]
> https://patchwork.freedesktop.org/patch/msgid/20210913175747.47456-14-sean@xxxxxxxxxx
> ---

/snip

> diff --git a/drivers/gpu/drm/msm/Makefile b/drivers/gpu/drm/msm/Makefile
> index 904535eda0c4..98731fd262d6 100644
> --- a/drivers/gpu/drm/msm/Makefile
> +++ b/drivers/gpu/drm/msm/Makefile
> @@ -109,6 +109,7 @@ msm-$(CONFIG_DRM_MSM_DP)+= dp/dp_aux.o \
>  	dp/dp_ctrl.o \
>  	dp/dp_display.o \
>  	dp/dp_drm.o \
> +	dp/dp_hdcp.o \
>  	dp/dp_hpd.o \
>  	dp/dp_link.o \
>  	dp/dp_panel.o \
> diff --git a/drivers/gpu/drm/msm/dp/dp_debug.c
> b/drivers/gpu/drm/msm/dp/dp_debug.c
> index 2f6247e80e9d..de16fca8782a 100644
> --- a/drivers/gpu/drm/msm/dp/dp_debug.c
> +++ b/drivers/gpu/drm/msm/dp/dp_debug.c

/snip

> +static ssize_t dp_hdcp_key_write(struct file *file, const char __user
> *ubuf,
> +				 size_t len, loff_t *offp)
> +{
> +	char *input_buffer;
> +	int ret = 0;
> +	struct dp_debug_private *debug = file->private_data;
> +	struct drm_device *dev;
> +
> +	dev = debug->drm_dev;
> +
> +	if (len != (DRM_HDCP_KSV_LEN + DP_HDCP_NUM_KEYS * DP_HDCP_KEY_LEN))
> +		return -EINVAL;
> +
> +	if (!debug->hdcp)
> +		return -ENOENT;
> +
> +	input_buffer = memdup_user_nul(ubuf, len);
> +	if (IS_ERR(input_buffer))
> +		return PTR_ERR(input_buffer);
> +
> +	ret = dp_hdcp_ingest_key(debug->hdcp, input_buffer, len);
> +
> +	kfree(input_buffer);
> +	if (ret < 0) {
> +		DRM_ERROR("Could not ingest HDCP key, ret=%d\n", ret);
> +		return ret;
> +	}
> +
> +	*offp += len;
> +	return len;
> +}

It seems like the HDCP keys written using debugfs, just for my
understanding,
are you storing this in some secure partition and the usermode reads from it
and writes them here?


We have not sorted out the userspace side of HDCP enablement yet, so it remains to be seen whether the keys will be injected via debugfs/firmware file/property.

/snip

> +static int dp_connector_atomic_check(struct drm_connector *connector,
> +				     struct drm_atomic_state *state)
> +{
> +	struct drm_connector_state *conn_state;
> +	struct dp_connector_state *dp_state;
> +
> +	conn_state = drm_atomic_get_new_connector_state(state, connector);
> +	dp_state = to_dp_connector_state(conn_state);
> +
> +	dp_state->hdcp_transition = drm_hdcp_atomic_check(connector, state);

I have a general question related to the transition flag and overall tying
the HDCP
enable and authentication to the commit.
So lets say there is a case where the driver needs to disable HDCP. It could
be due
to link integrity failure OR some other error condition which usermode is
not aware of.
In that case, we will set this hdcp_transition to true but in the next
commit we will
actually do the authentication. What if usermode doesnt issue a new frame? This question arises because currently the link intergrity check is done
using SW polling
in the previous patchset. But as I had commented there, this occurs in HW
for us.
I dont see that isr itself in this patchset. So wanted to understand if
thats part of this
approach to still tie it with commit.

So if we go with the HW polling based approach which is the preferred
method, we need to
untie this from the commit.


In the case of error, the worker will detect it and try to re-authenticate. If the re-authentication is successful, userspace will continue to be unaware and everything will keep working. If re-authentication is unsuccessful, the worker
will update the property value and issue a uevent to userspace. So HDCP
enablement is only tied to commits when the property value is changing as a
result of userspace.

Regarding SW vs HW link checks, I don't think there's any difference in efficacy between them. If HW can be relied on to issue an interrupt in failure cases, a
follow-up set allowing for this seems like a great idea.


Thanks for the explanation. Yes, from our experience it has been pretty reliable to issue signal integrity failures. We already had the isr based approach downstream and would prefer to keep it that way based on our experience of it firing reliably. We can still keep the SW polling code but it should come into effect only if HW polling
is not supported / preferred.

> +
> +	return 0;
> +}

/snip

> +static int dp_hdcp_load_keys(struct drm_connector *connector)
> +{
> +	struct dp_hdcp *hdcp = dp_display_connector_to_hdcp(connector);
> +	struct dp_hdcp_key *key;
> +	int i, ret = 0;
> +
> +	mutex_lock(&hdcp->key_lock);
> +
> +	key = hdcp->key;
> +
> +	if (!key->valid) {
> +		ret = -ENOENT;
> +		goto out;
> +	}
> +
> +	dp_hdcp_write_dp(hdcp, DP_HDCP_SW_LOWER_AKSV, key->ksv.words[0]);
> +	dp_hdcp_write_dp(hdcp, DP_HDCP_SW_UPPER_AKSV, key->ksv.words[1]);
> +
> +	for (i = 0; i < DP_HDCP_NUM_KEYS; i++) {
> +		dp_hdcp_write_hdcp(hdcp, DP_HDCP_KEY_LSB(i),
> +				   key->keys[i].words[0]);
> +		dp_hdcp_write_hdcp(hdcp, DP_HDCP_KEY_MSB(i),
> +				   key->keys[i].words[1]);
> +	}
> +
> +	dp_hdcp_write_hdcp(hdcp, DP_HDCP_KEY_VALID, DP_HDCP_SW_KEY_VALID);

I think all of these are TZ_*** registers. So the separation of write_hdcp()
Vs write_hdcp_tz()
is not very clear to me.
Maybe change the write APIs to something like dp_hdcp_write_hdcp_tz() for
the first address space
and dp_hdcp_write_hdcp_tz_hlos() for the other one?


Will do in v3, thank you for the suggestion.

> +	wmb();
> +
> +	dp_hdcp_write_dp(hdcp, DP_HDCP_ENTROPY_CTRL0, get_random_u32());
> +	dp_hdcp_write_dp(hdcp, DP_HDCP_ENTROPY_CTRL1, get_random_u32());
> +	wmb();
> +
> +out:
> +	mutex_unlock(&hdcp->key_lock);
> +	return ret;
> +}
> +
> +static int dp_hdcp_hdcp2_capable(struct drm_connector *connector,
> bool *capable)
> +{
> +	*capable = false;
> +	return 0;
> +}
> +
> +static int dp_hdcp_hdcp1_read_an_aksv(struct drm_connector *connector,
> +				      u32 *an, u32 *aksv)
> +{
> +	struct dp_hdcp *hdcp = dp_display_connector_to_hdcp(connector);
> +	bool keys_valid;
> +	int ret;
> +	u32 val;
> +
> +	dp_hdcp_write_dp(hdcp, DP_HDCP_CTRL, 1);
> +
> +	ret = read_poll_timeout(dp_hdcp_are_keys_valid, keys_valid,
> keys_valid,
> +				20 * 1000, 10 * 1000, false, connector);
> +	if (ret) {
> +		drm_err(hdcp->dev, "HDCP keys invalid %d\n", ret);
> +		return ret;
> +	}
> +
> +	/* Clear AInfo */
> +	dp_hdcp_write_dp(hdcp, DP_HDCP_RCVPORT_DATA4, 0);
> +
> +	aksv[0] = dp_hdcp_read_dp(hdcp, DP_HDCP_RCVPORT_DATA3);
> +	aksv[1] = GENMASK(7, 0) & dp_hdcp_read_dp(hdcp,
> DP_HDCP_RCVPORT_DATA4);
> +
> +	ret = read_poll_timeout(dp_hdcp_read_dp, val,
> +				(val & DP_HDCP_AN_READY_MASK) == DP_HDCP_AN_READY_MASK,
> +				100, 10 * 1000, false, hdcp, DP_HDCP_STATUS);
> +	if (ret) {
> +		drm_err(hdcp->dev, "AN failed to become ready %x/%d\n", val, ret);
> +		return ret;
> +	}
> +
> +	/*
> +	 * Get An from hardware, for unknown reasons we need to read the reg
> +	 * twice to get valid data.
> +	 */
> +	dp_hdcp_read_dp(hdcp, DP_HDCP_RCVPORT_DATA5);
> +	an[0] = dp_hdcp_read_dp(hdcp, DP_HDCP_RCVPORT_DATA5);
> +
> +	dp_hdcp_read_dp(hdcp, DP_HDCP_RCVPORT_DATA6);
> +	an[1] = dp_hdcp_read_dp(hdcp, DP_HDCP_RCVPORT_DATA6);

Yes its true, but we also have a 1 microsec delay between the first and
second one.
So I would certainly preserve that.

Will do in v3, thank you for the suggestion.


> +
> +	return 0;
> +}
> +
> +static int dp_hdcp_hdcp1_store_receiver_info(struct drm_connector
> *connector,
> +					     u32 *ksv, u32 status, u8 bcaps,
> +					     bool is_repeater)
> +{
> +	struct dp_hdcp *hdcp = dp_display_connector_to_hdcp(connector);
> +	u32 val;
> +
> +	dp_hdcp_write_tz(hdcp, HDCP_SEC_DP_TZ_HV_HLOS_HDCP_RCVPORT_DATA0,
> +			 ksv[0]);
> +	dp_hdcp_write_tz(hdcp, HDCP_SEC_DP_TZ_HV_HLOS_HDCP_RCVPORT_DATA1,
> +			 ksv[1]);
> +
> +	val = ((status & GENMASK(15, 0)) << 8) | (bcaps & GENMASK(7, 0));
> +
> +	dp_hdcp_write_tz(hdcp, HDCP_SEC_DP_TZ_HV_HLOS_HDCP_RCVPORT_DATA12,
> val);
> +

Cant this entire API be skipped for non-repeater cases from the hdcp lib
layer?
You can write the bcaps to this earlier and write the bstatus only if its a
repeater.

Could you expand on the benefits of this?

We can avoid the call coming into the vendor driver hook itself as it need not be called for non-repeater cases. So something like this can be done in the HDCP lib?

if ( repeater && ops->hdcp1_store_receiver_info )
     ops->hdcp1_store_receiver_info(....);



> +	return 0;
> +}

/snip



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