linux-kernel - Re: [PATCH 2/2] mmc: dw_mmc: add resets support to dw_mci_parse

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Message-ID: <56D904F5.9020700@rock-chips.com>
Date:	Fri, 4 Mar 2016 11:45:57 +0800
From:	Shawn Lin <shawn.lin@...k-chips.com>
To:	zhangfei <zhangfei.gao@...aro.org>,
	Guodong Xu <guodong.xu@...aro.org>, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	jh80.chung@...sung.com, ulf.hansson@...aro.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mmc@...r.kernel.org
Cc:	shawn.lin@...k-chips.com, shawn.lin@...nel-upstream.org,
	Xinwei Kong <kong.kongxinwei@...ilicon.com>
Subject: Re: [PATCH 2/2] mmc: dw_mmc: add resets support to dw_mci_parse_dt()

在 2016/3/4 11:27, zhangfei 写道:
>
>
> On 03/03/2016 10:00 AM, Shawn Lin wrote:
>> Hi Guodong,
>>
>> On 2016/3/3 9:33, Guodong Xu wrote:
>>> With this, user can add a 'resets' property into dw_mmc dts
>>> node, and when driver probe and parse_dt, it will call
>>> reset APIs to reset dw_mmc host controller.
>>>
>>> Please also refer to Documentation/devicetree/bindings/reset/reset.txt
>>
>> I have no hard objection for this patch, but I'd rather not add it
>> unless we actually need it. Could you elaborate more about any futher
>> actions you will take if it's applied(i.e: deal with some unrecoverable
>> broken case)?  If we just reset the controller while probing, actually I
>> can't find any problems without it based on tons of my reboot test.
>
> mmc register maybe abnormal state, if mmc is used in uefi, like boot
> from emmc.
> So we need reset mmc register when kernel boot up, instead of assuming
> mmc is in clean state.
> Next step is adding reset node in dts for drivers/mmc/host/dw_mmc-k3.c
> as reset driver is already there.

Fair enough. Thanks for explaining.

>
>>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>>> index 242f9a0..d3a7376 100644
>>> --- a/drivers/mmc/host/dw_mmc.c
>>> +++ b/drivers/mmc/host/dw_mmc.c
>>> @@ -2878,6 +2878,13 @@ static struct dw_mci_board
>>> *dw_mci_parse_dt(struct dw_mci *host)
>>>       if (!pdata)
>>>           return ERR_PTR(-ENOMEM);
>>>
>>> +    /* find reset controller when exist */
>>> +    pdata->rstc = devm_reset_control_get_optional(dev, NULL);
>>> +    if (IS_ERR(pdata->rstc))
>>> +        pdata->rstc = NULL;
>>> +    else
>>> +        reset_control_deassert(pdata->rstc);
>>> +
>>
>> if the PTR_ERR(pdata->rstc) is -EPROBE_DEFER, should we defer probing
>> the driver?
> Yes, good catch.
>
> Thanks
>
>
>


-- 
Best Regards
Shawn Lin