[Intel-gfx] [PATCH 4/6] drm: scrambling support in drm layer
Sharma, Shashank
shashank.sharma at intel.com
Thu Feb 2 05:38:22 UTC 2017
Regards
Shashank
On 2/1/2017 10:02 PM, Thierry Reding wrote:
> 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 at 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.
Agree.
>> + * 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.
Got it.
>> + *
>> + * 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.
Ok.
>> + */
>> +
>> +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.
Yeah, the same is mentioned by Ville too, will do that.
>> +{
>> + 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.
Agree, in fact while debugging and testing this patch series, I had to
print it explicitly.
>
>> + return false;
>> + }
>> +
>> + status &= SCDC_SCRAMBLING_STATUS;
>> + return status != 0;
> Maybe make this a single line:
>
> return (status & SCDC_SCRAMBLING_STATUS) != 0;
Got it.
>
>> +}
>> +
>> +/**
>> + * drm_enable_scrambling - enable scrambling
>> + * @connector: target drm_connector
> "target DRM connector"?
Got it.
>> + * @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.
Agree, will move it.
>> +{
>> + 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?
Ok.
>> + 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.
Ok
>> + 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().
Got it.
>> @@ -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".
Got it.
>> + */
>> + 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.
Agree, will change it.
>> + /**
>> + * @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.
Sure, can be done.
>
> 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?
My opinion while designing was:
- SCDC rr support is platform specific, and a platform can choose not to
support read_req but just allow
scrambling using scdc read and write, hence kept that separate
- You need to look into this internal structure, only if scdc is supported.
- Also, SCDC registers can be used beyond scrambling too, like for error
detection, and other cases, so I thought
it would be better to keep it independent.
Does it make sense ?
-Shashank
>
> 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
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