[PATCH 4/4] drm/bridge: dw-hdmi: add cec driver

[Hans Verkuil]

On 06/02/17 08:43, Jose Abreu wrote:
> Hi Hans,
> 
> 
> On 02-06-2017 07:31, Hans Verkuil wrote:
>> On 06/01/2017 03:47 PM, Neil Armstrong wrote:
>>> On 05/30/2017 04:23 PM, Russell King wrote:
>>>> Add a CEC driver for the dw-hdmi hardware.
>>>>
>>>> Signed-off-by: Russell King <rmk+kernel at armlinux.org.uk>
>>>> ---
>>>>   drivers/gpu/drm/bridge/synopsys/Kconfig       |   8 +
>>>>   drivers/gpu/drm/bridge/synopsys/Makefile      |   1 +
>>>>   drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.c | 320
>>>> ++++++++++++++++++++++++++
>>>>   drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.h |  19 ++
>>>>   drivers/gpu/drm/bridge/synopsys/dw-hdmi.c     |  40 +++-
>>>>   5 files changed, 387 insertions(+), 1 deletion(-)
>>>>   create mode 100644
>>>> drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.c
>>>>   create mode 100644
>>>> drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.h
>>>>
>>>> diff --git a/drivers/gpu/drm/bridge/synopsys/Kconfig
>>>> b/drivers/gpu/drm/bridge/synopsys/Kconfig
>>>> index 40d2827a6d19..bd30a0a07272 100644
>>>> --- a/drivers/gpu/drm/bridge/synopsys/Kconfig
>>>> +++ b/drivers/gpu/drm/bridge/synopsys/Kconfig
>>>> @@ -21,3 +21,11 @@ config DRM_DW_HDMI_I2S_AUDIO
>>>>       help
>>>>         Support the I2S Audio interface which is part of the
>>>> Synopsys
>>>>         Designware HDMI block.
>>>> +
>>>> +config DRM_DW_HDMI_CEC
>>>> +    tristate "Synopsis Designware CEC interface"
>>>> +    depends on DRM_DW_HDMI && MEDIA_CEC_SUPPORT
>>>> +    select MEDIA_CEC_NOTIFIER
>>>> +    help
>>>> +      Support the CE interface which is part of the Synopsis
>>>> +      Designware HDMI block.
>>>> diff --git a/drivers/gpu/drm/bridge/synopsys/Makefile
>>>> b/drivers/gpu/drm/bridge/synopsys/Makefile
>>>> index 17aa7a65b57e..6fe415903668 100644
>>>> --- a/drivers/gpu/drm/bridge/synopsys/Makefile
>>>> +++ b/drivers/gpu/drm/bridge/synopsys/Makefile
>>>> @@ -3,3 +3,4 @@
>>>>   obj-$(CONFIG_DRM_DW_HDMI) += dw-hdmi.o
>>>>   obj-$(CONFIG_DRM_DW_HDMI_AHB_AUDIO) += dw-hdmi-ahb-audio.o
>>>>   obj-$(CONFIG_DRM_DW_HDMI_I2S_AUDIO) += dw-hdmi-i2s-audio.o
>>>> +obj-$(CONFIG_DRM_DW_HDMI_CEC) += dw-hdmi-cec.o
>>>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.c
>>>> b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.c
>>>> new file mode 100644
>>>> index 000000000000..761ef5ae687d
>>>> --- /dev/null
>>>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.c
>>>> @@ -0,0 +1,320 @@
>>>> +/*
>>>> + * Designware HDMI CEC driver
>>>> + *
>>>> + * Copyright (C) 2015-2017 Russell King.
>>>> + *
>>>> + * This program is free software; you can redistribute it
>>>> and/or modify
>>>> + * it under the terms of the GNU General Public License
>>>> version 2 as
>>>> + * published by the Free Software Foundation.
>>>> + */
>>>> +#include <linux/interrupt.h>
>>>> +#include <linux/io.h>
>>>> +#include <linux/module.h>
>>>> +#include <linux/platform_device.h>
>>>> +#include <linux/sched.h>
>>>> +#include <linux/slab.h>
>>>> +
>>>> +#include <drm/drm_edid.h>
>>>> +
>>>> +#include <media/cec.h>
>>>> +#include <media/cec-notifier.h>
>>>> +
>>>> +#include "dw-hdmi-cec.h"
>>>> +
>>>> +enum {
>>>> +    HDMI_IH_CEC_STAT0    = 0x0106,
>>>> +    HDMI_IH_MUTE_CEC_STAT0    = 0x0186,
>>>> +
>>>> +    HDMI_CEC_CTRL        = 0x7d00,
>>>> +    CEC_CTRL_START        = BIT(0),
>>>> +    CEC_CTRL_NORMAL        = 1 << 1,
>>>> +
>>>> +    HDMI_CEC_STAT        = 0x7d01,
>>>> +    CEC_STAT_DONE        = BIT(0),
>>>> +    CEC_STAT_EOM        = BIT(1),
>>>> +    CEC_STAT_NACK        = BIT(2),
>>>> +    CEC_STAT_ARBLOST    = BIT(3),
>>>> +    CEC_STAT_ERROR_INIT    = BIT(4),
>>>> +    CEC_STAT_ERROR_FOLL    = BIT(5),
>>>> +    CEC_STAT_WAKEUP        = BIT(6),
>>
>> I hadn't realized until Jose Abreu's latest reply, but you need
>> to check the
>> ARBLOST status and set the TX state to CEC_TX_STATUS_ARB_LOST.
>>
>> I think CEC_STAT_ERROR_FOLL might equal
>> CEC_TX_STATUS_LOW_DRIVE, but without
>> documentation I can't be sure.
>>
>> My experience is that this low drive condition tends to be
>> poorly reported by
>> hardware. Either that or poorly documented. This is why I added a
>> CEC_TX_STATUS_ERROR status as a catch-all error status when it
>> is unclear from
>> the hardware/documentation what error occurred.
>>
>> Jose, do you know which status bit is used to report a follower
>> pulling the
>> CEC line low for a long time (approx. 3.6 ms) to signal a CEC
>> error?
> 
> Bit 5 for follower error, bit 4 for initiator error.

I gathered that from the define names :-)

But what does it mean? What sort of error is reported here?

I'm guessing here that "follower error" means that one of the remote
CEC devices forced a Low Drive condition, where "initiator error"
means that our adapter forced a Low Drive condition on the bus.

Would that be correct?

If so, then the CEC_STAT_ERROR_INIT can be ignored and ERROR_FOLL
maps to the LOW_DRIVE status.

(Low Drive condition is what is described in section CEC 7.4 "CEC Line
Error Handling" of the HDMI 1.4 Specification).

Regards,

	Hans