linux-kernel - Re: [PATCH v2 1/5] drm: bridge: dw_hdmi: cec: Add cec suspend/resume function

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Message-ID: <41211991-e755-21d8-1c94-62d91401d0c6@baylibre.com>
Date:   Mon, 11 Apr 2022 09:42:28 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Jernej Škrabec <jernej.skrabec@...il.com>,
        Sandor Yu <Sandor.yu@....com>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, andrzej.hajda@...el.com,
        robert.foss@...aro.org, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, hverkuil-cisco@...all.nl
Cc:     shengjiu.wang@....com, cai.huoqing@...ux.dev, maxime@...no.tech,
        harry.wentland@....com
Subject: Re: [PATCH v2 1/5] drm: bridge: dw_hdmi: cec: Add cec suspend/resume
 function

On 10/04/2022 12:13, Jernej Škrabec wrote:
> Dne petek, 08. april 2022 ob 15:41:36 CEST je Neil Armstrong napisal(a):
>> On 08/04/2022 12:32, Sandor Yu wrote:
>>> CEC interrupt status/mask and logical address registers
>>> will be reset when device enter suspend.
>>> It will cause cec fail to work after device resume.
>>> Add CEC suspend/resume functions, reinitialize logical address registers
>>> and restore interrupt status/mask registers after resume.
>>>
>>> Signed-off-by: Sandor Yu <Sandor.yu@....com>
>>> ---
>>>
>>>    drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.c | 37 +++++++++++++++++++
>>>    1 file changed, 37 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.c
>>> b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.c index
>>> c8f44bcb298a..ab176401b727 100644
>>> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.c
>>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-cec.c
>>> @@ -62,6 +62,10 @@ struct dw_hdmi_cec {
>>>
>>>    	bool rx_done;
>>>    	struct cec_notifier *notify;
>>>    	int irq;
>>>
>>> +
>>> +	u8 regs_polarity;
>>> +	u8 regs_mask;
>>> +	u8 regs_mute_stat0;
>>>
>>>    };
>>>    
>>>    static void dw_hdmi_write(struct dw_hdmi_cec *cec, u8 val, int offset)
>>>
>>> @@ -306,11 +310,44 @@ static int dw_hdmi_cec_remove(struct platform_device
>>> *pdev)>
>>>    	return 0;
>>>    
>>>    }
>>>
>>> +static int __maybe_unused dw_hdmi_cec_resume(struct device *dev)
>>> +{
>>> +	struct dw_hdmi_cec *cec = dev_get_drvdata(dev);
>>> +
>>> +	/* Restore logical address */
>>> +	dw_hdmi_write(cec, cec->addresses & 255, HDMI_CEC_ADDR_L);
>>> +	dw_hdmi_write(cec, cec->addresses >> 8, HDMI_CEC_ADDR_H);
>>> +
>>> +	/* Restore interrupt status/mask register */
>>> +	dw_hdmi_write(cec, cec->regs_polarity, HDMI_CEC_POLARITY);
>>> +	dw_hdmi_write(cec, cec->regs_mask, HDMI_CEC_MASK);
>>> +	dw_hdmi_write(cec, cec->regs_mute_stat0, HDMI_IH_MUTE_CEC_STAT0);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static int __maybe_unused dw_hdmi_cec_suspend(struct device *dev)
>>> +{
>>> +	struct dw_hdmi_cec *cec = dev_get_drvdata(dev);
>>> +
>>> +	/* store interrupt status/mask register */
>>> +	 cec->regs_polarity = dw_hdmi_read(cec, HDMI_CEC_POLARITY);
>>> +	 cec->regs_mask = dw_hdmi_read(cec, HDMI_CEC_MASK);
>>> +	 cec->regs_mute_stat0 = dw_hdmi_read(cec, HDMI_IH_MUTE_CEC_STAT0);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static const struct dev_pm_ops dw_hdmi_cec_pm = {
>>> +	SET_SYSTEM_SLEEP_PM_OPS(dw_hdmi_cec_suspend, dw_hdmi_cec_resume)
>>> +};
>>> +
>>>
>>>    static struct platform_driver dw_hdmi_cec_driver = {
>>>    
>>>    	.probe	= dw_hdmi_cec_probe,
>>>    	.remove	= dw_hdmi_cec_remove,
>>>    	.driver = {
>>>    	
>>>    		.name = "dw-hdmi-cec",
>>>
>>> +		.pm = &dw_hdmi_cec_pm,
>>>
>>>    	},
>>>    
>>>    };
>>>    module_platform_driver(dw_hdmi_cec_driver);
>>
>> As Hans said on v1, why don't you call dw_hdmi_cec_enable(cec->adap, false)
>> in suspend and dw_hdmi_cec_enable(cec->adap, true) in resume ?
>>
>> With this, CEC engine is not disabled on suspend.
> 
> This should not be done, at least not unconditionally. CEC wakeup
> functionality is used by Crust firmware for Allwinner boards. In fact, DW HDMI
> CEC controller was designed with suspend/resume functionality in mind. If
> properly set, it can autonomously scan for preset CEC messages and generate
> interrupt when found.
> 
> Actually, I'm not fan of this patch, since it looks like workaround for power
> management firmware not restoring previous state. Or is this HW issue? In any
> case, Allwinner SoCs with DW-HDMI CEC don't need restoring any register, so
> it's certainly not a general issue.

In this case I think it should explicit in the hdmi_plat_data to either let
CEC enabled on suspend or then disable CEC on suspend.

> 
>>
>> Do you plan to use the engine from the suspend code ?
> 
> As mentioned before, it's already done for Allwinner, so CEC should remain
> enabled

Thanks for confirming that

> 
> Best regards,
> Jernej
> 
>>
>> Neil
> 
> 
> 
> 

Neil