Re: [PATCH 4/6] drm: scrambling support in drm layer

[Thierry Reding <thierry.reding@gmail.com>]

[-- Attachment #1.1: Type: text/plain, Size: 8653 bytes --]

On Wed, Feb 01, 2017 at 06:14:39PM +0530, Shashank Sharma wrote:
> HDMI 2.0 spec mandates scrambling for modes with pixel clock higher
> than 340Mhz. This patch adds few new functions in drm layer for
> core drivers to enable/disable scrambling.
> 
> This patch adds:
> - A function to detect scrambling support parsing HF-VSDB
> - A function to check scrambling status runtime using SCDC read.
> - Two functions to enable/disable scrambling using SCDC read/write.
> - Few new bools to reflect scrambling support and status.
> 
> Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
> ---
>  drivers/gpu/drm/drm_edid.c  | 131 +++++++++++++++++++++++++++++++++++++++++++-
>  include/drm/drm_connector.h |  24 ++++++++
>  include/drm/drm_edid.h      |   6 +-
>  3 files changed, 159 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 37902e5..f0d940a 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -37,6 +37,7 @@
>  #include <drm/drm_edid.h>
>  #include <drm/drm_encoder.h>
>  #include <drm/drm_displayid.h>
> +#include <drm/drm_scdc_helper.h>
>  
>  #define version_greater(edid, maj, min) \
>  	(((edid)->version > (maj)) || \
> @@ -3814,6 +3815,132 @@ static void drm_detect_hdmi_scdc(struct drm_connector *connector,
>  	}
>  }
>  
> +static void drm_detect_hdmi_scrambling(struct drm_connector *connector,
> +				 const u8 *hf_vsdb)
> +{
> +	struct drm_display_info *display = &connector->display_info;
> +	struct drm_hdmi_info *hdmi = &display->hdmi_info;
> +
> +	/*
> +	 * All HDMI 2.0 monitors must support scrambling at rates > 340M.

In comments below you use Mhz as the abbreviations. This should be
consistent. Also I think "MHz" is actually the correct spelling.

> +	 * And as per the spec, three factors confirm this:
> +	 * * Availability of a HF-VSDB block in EDID (check)
> +	 * * Non zero Max_TMDS_Char_Rate filed in HF-VSDB
> +	 * * SCDC support available
> +	 * Lets check it out.
> +	 */
> +
> +	if (hf_vsdb[5]) {
> +		display->max_tmds_clock = hf_vsdb[5] * 5000;
> +		DRM_DEBUG_KMS("HF-VSDB: max TMDS clock %d kHz\n",
> +			display->max_tmds_clock);
> +
> +		if (hdmi->scdc_supported) {
> +			hdmi->scr_info.supported = true;
> +
> +			/* Few sinks support scrambling for cloks < 340M */
> +			if ((hf_vsdb[6] & 0x8))
> +				hdmi->scr_info.low_clocks = true;
> +		}
> +	}
> +}
> +
> +/**
> + * drm_check_scrambling_status - what is status of scrambling?
> + * @adapter: i2c adapter for SCDC channel

"I2C", same in other parts of this patch.

> + *
> + * Read the scrambler status over SCDC channel, and check the
> + * scrambling status.
> + *
> + * Return: True if the scrambling is enabled, false otherwise.

I think the rest of DRM/KMS kerneldoc tries to use "Returns:\n" as a
standard way to document return values.

> + */
> +
> +bool drm_check_scrambling_status(struct i2c_adapter *adapter)

Maybe use a drm_scdc_*() prefix for this to make it more consistent with
other SCDC API.

While at it, would this not be better located in drm_scdc.c along with
the other helpers? drm_edid.c is more focussed on the parsing aspects of
all things EDID.

> +{
> +	u8 status;
> +
> +	if (drm_scdc_readb(adapter, SCDC_SCRAMBLER_STATUS, &status) < 0) {

How about storing the error code...

> +		DRM_ERROR("Failed to read scrambling status\n");

... and making it part of the error message? Sometimes its useful to
know what exact error triggered this because it helps narrowing down
where things went wrong.

> +		return false;
> +	}
> +
> +	status &= SCDC_SCRAMBLING_STATUS;
> +	return status != 0;

Maybe make this a single line:

	return (status & SCDC_SCRAMBLING_STATUS) != 0;

> +}
> +
> +/**
> + * drm_enable_scrambling - enable scrambling
> + * @connector: target drm_connector

"target DRM connector"?

> + * @adapter: i2c adapter for SCDC channel
> + * @force: enable scrambling, even if its already enabled
> + *
> + * Write the TMDS config over SCDC channel, and enable scrambling
> + * Return: True if scrambling is successfully enabled, false otherwise.
> + */
> +
> +bool drm_enable_scrambling(struct drm_connector *connector,
> +					struct i2c_adapter *adapter, bool force)

I think I'd move this to drm_scdc.c as well because it primarily
operates on SCDC. If you do so, might be worth making adapter the first
argument for consistency with other SCDC API.

> +{
> +	u8 config;
> +	struct drm_hdmi_info *hdmi_info = &connector->display_info.hdmi_info;
> +
> +	if (hdmi_info->scr_info.status && !force) {
> +		DRM_DEBUG_KMS("Scrambling already enabled\n");
> +		return true;
> +	}
> +
> +	if (drm_scdc_readb(adapter, SCDC_TMDS_CONFIG, &config) < 0) {
> +		DRM_ERROR("Failed to read tmds config\n");

Maybe also print the error code?

> +		return false;
> +	}
> +
> +	config |= SCDC_SCRAMBLING_ENABLE;
> +
> +	if (drm_scdc_writeb(adapter, SCDC_TMDS_CONFIG, config) < 0) {
> +		DRM_ERROR("Failed to enable scrambling, write error\n");

Same here.

> +		return false;
> +	}
> +
> +	hdmi_info->scr_info.status = drm_check_scrambling_status(adapter);
> +	return hdmi_info->scr_info.status;
> +}
> +
> +/**
> + * drm_disable_scrambling - disable scrambling
> + * @connector: target drm_connector
> + * @adapter: i2c adapter for SCDC channel
> + * @force: disable scrambling, even if its already disabled
> + *
> + * Write the TMDS config over SCDC channel, and disable scrambling
> + * Return: True if scrambling is successfully disabled, false otherwise.
> + */
> +bool drm_disable_scrambling(struct drm_connector *connector,
> +					struct i2c_adapter *adapter, bool force)
> +{
> +	u8 config;
> +	struct drm_hdmi_info *hdmi_info = &connector->display_info.hdmi_info;
> +
> +	if (!hdmi_info->scr_info.status && !force) {
> +		DRM_DEBUG_KMS("Scrambling already disabled\n");
> +		return true;
> +	}
> +
> +	if (drm_scdc_readb(adapter, SCDC_TMDS_CONFIG, &config) < 0) {
> +		DRM_ERROR("Failed to read tmds config\n");
> +		return false;
> +	}
> +
> +	config &= ~SCDC_SCRAMBLING_ENABLE;
> +
> +	if (drm_scdc_writeb(adapter, SCDC_TMDS_CONFIG, config) < 0) {
> +		DRM_ERROR("Failed to enable scrambling, write error\n");
> +		return false;
> +	}
> +
> +	hdmi_info->scr_info.status = drm_check_scrambling_status(adapter);
> +	return !hdmi_info->scr_info.status;
> +}

Same comments as for drm_enable_scrambling().

> @@ -3928,8 +4055,10 @@ static void drm_parse_cea_ext(struct drm_connector *connector,
>  
>  		if (cea_db_is_hdmi_vsdb(db))
>  			drm_parse_hdmi_vsdb_video(connector, db);
> -		if (cea_db_is_hdmi_forum_vsdb(db))
> +		if (cea_db_is_hdmi_forum_vsdb(db)) {
>  			drm_detect_hdmi_scdc(connector, db);
> +			drm_detect_hdmi_scrambling(connector, db);
> +		}
>  	}
>  }
>  
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 2435598..b9735bd 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -90,6 +90,26 @@ enum subpixel_order {
>  
>  };
>  
> +
> +/**
> + * struct scrambling: sink's scrambling support.
> + */
> +struct scrambling {
> +	/**
> +	 * @supported: scrambling supported for rates > 340Mhz.

I think it's common to separate number and unit by a space, so "340
MHz".

> +	 */
> +	bool supported;
> +	/**
> +	 * @low_clocks: scrambling supported for rates <= 340Mhz.
> +	 */
> +	bool low_clocks;

Maybe "low_rates" because a clock is technically the source of a signal
that oscillates at the given rate.

> +	/**
> +	 * @status: scrambling enabled/disabled ?
> +	 */
> +	bool status;
> +};
> +
> +
>  /**
>   * struct drm_hdmi_info - runtime data about the connected sink
>   *
> @@ -108,6 +128,10 @@ struct drm_hdmi_info {
>  	 * @scdc_rr: sink is capable of generating scdc read request.
>  	 */
>  	bool scdc_rr;
> +	/**
> +	 * scr_info: sink's scrambling support and capabilities.
> +	 */
> +	struct scrambling scr_info;

Again, I think I'd drop _info and instead spell out "scrambling" to make
this easier to remember.

Also I'm wondering why scdc_supported and scdc_rr are not in a structure
if scrambling info is. Also since scrambling depends on SCDC, would it
make sense to embed it in a struct drm_hdmi_scdc_info?

	struct drm_hdmi_scdc_scrambling_info {
		bool supported;
		bool low_rates;
		bool status;
	};

	struct drm_hdmi_scdc_info {
		bool supported;
		bool read_request;

		struct drm_hdmi_scdc_scrambling_info scrambling;
	};

Thierry

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[-- Attachment #2: Type: text/plain, Size: 160 bytes --]

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel