linux-kernel - Re: [PATCH 1/2] drm/bridge/synopsys: dw-hdmi: Add an option to suppress loading CEC driver

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Message-ID: <5C989247.6090709@baylibre.com>
Date:   Mon, 25 Mar 2019 09:33:11 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Jernej Skrabec <jernej.skrabec@...l.net>
CC:     maxime.ripard@...tlin.com, airlied@...ux.ie,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        wens@...e.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] drm/bridge/synopsys: dw-hdmi: Add an option to suppress
 loading CEC driver



Le 25/03/2019 02:35, Laurent Pinchart a écrit :
> Hi Jernej,
> 
> Thank you for the patch.
> 
> On Sun, Mar 24, 2019 at 10:21:42PM +0100, Jernej Skrabec wrote:
>> DW HDMI controller on some Allwinner SoCs has support for CEC, but due
>> to additional logic put between CEC controller and pins, it doesn't work
>> correctly, at least not with a lot of instrusive changes. Fortunately,
>> it's still possible to bitbang protocol.
>>
>> For such cases, add a platform option to suppress loading CEC driver. If
>> DW HDMI CEC driver would be loaded, it wouldn't work anyway and only
>> cause a confusion with multiple /dev entries.
>>
>> Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
>> ---
>>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 2 +-
>>  include/drm/bridge/dw_hdmi.h              | 2 ++
>>  2 files changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> index a63e5f0dae56..fdda26f8b056 100644
>> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> @@ -2634,7 +2634,7 @@ __dw_hdmi_probe(struct platform_device *pdev,
>>  		hdmi->audio = platform_device_register_full(&pdevinfo);
>>  	}
>>  
>> -	if (config0 & HDMI_CONFIG0_CEC) {
>> +	if (!plat_data->is_cec_unusable && (config0 & HDMI_CONFIG0_CEC)) {
>>  		cec.hdmi = hdmi;
>>  		cec.ops = &dw_hdmi_cec_ops;
>>  		cec.irq = irq;
>> diff --git a/include/drm/bridge/dw_hdmi.h b/include/drm/bridge/dw_hdmi.h
>> index 66e70770cce5..764b8bcfa62c 100644
>> --- a/include/drm/bridge/dw_hdmi.h
>> +++ b/include/drm/bridge/dw_hdmi.h
>> @@ -144,6 +144,8 @@ struct dw_hdmi_plat_data {
>>  	int (*configure_phy)(struct dw_hdmi *hdmi,
>>  			     const struct dw_hdmi_plat_data *pdata,
>>  			     unsigned long mpixelclock);
>> +
>> +	unsigned int is_cec_unusable : 1;
> 
> Strictly speaking your CEC controller isn't unusable, it's just a bit
> difficult to use it according to your commit message. Would disable_cec
> be a more appropriate field name ? 

Actually, it would be useful to have in for Amlogic SoCs also, the dw-hdmi
is configured with the CEC engine, but isn't connected to an external I/O.
And we have easy way to disable it unless disabling the DW-HDMI CEC driver...
With a more appropriate name,
Reviewed-by: Neil Armstrong <narmstrong@...libre.com>

> And how difficult would it be to
> support the hardware CEC controller, would that result in changes that
> could be useful to other vendors too ?
> 
>>  };
>>  
>>  struct dw_hdmi *dw_hdmi_probe(struct platform_device *pdev,
>