linux-kernel - Re: [PATCH v2 06/14] mmc: dw_mmc: simplify optional reset handling

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Message-id: <5f6c8c58-c4e4-39e6-2c29-e889bd6bf565@samsung.com>
Date:   Mon, 20 Mar 2017 11:49:22 +0100
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Philipp Zabel <p.zabel@...gutronix.de>
Cc:     linux-mmc@...r.kernel.org, Jaehoon Chung <jh80.chung@...sung.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-kernel@...r.kernel.org,
        "Szyprowski, Marek" <m.szyprowski@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH v2 06/14] mmc: dw_mmc: simplify optional reset handling

On 20.03.2017 11:27, Philipp Zabel wrote:
> Hi Andrzej,
>
> On Mon, 2017-03-20 at 11:03 +0100, Andrzej Hajda wrote:
>> Hi Philipp,
>>
>> On 20.03.2017 10:53, Philipp Zabel wrote:
>>> On Mon, 2017-03-20 at 10:22 +0100, Andrzej Hajda wrote:
>>>> Hi Philipp,
>>>>
>>>> Todays next branch does not work with exynos5433-tm2 board.
>>>> I guess this patch causes regression. On MMC without reset controller I
>>>> get errors:
>>>> [    4.938222] dwmmc_exynos 15540000.mshc: platform data not available
>>>> [    4.943268] dwmmc_exynos: probe of 15540000.mshc failed with error -22
> I was thrown off by this. Should maybe dw_mci_probe return the error
> value reported by dw_mci_parse_dt instead of always returning -EINVAL?
>
>>>> [    4.950184] dwmmc_exynos 15560000.mshc: platform data not available
>>>> [    4.955962] dwmmc_exynos: probe of 15560000.mshc failed with error -22
>>>>
>>>> Commenting out reset controller get and error checks 'fixes' the issue.
>>>>
>>>> On 15.03.2017 12:31, Philipp Zabel wrote:
>>>>> As of commit bb475230b8e5 ("reset: make optional functions really
>>>>> optional"), the reset framework API calls use NULL pointers to describe
>>>>> optional, non-present reset controls.
>>>>>
>>>>> This allows to return errors from devm_reset_control_get_optional and to
>>>>> call reset_control_(de)assert unconditionally.
>>>>>
>>>>> Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
>>>>> ---
>>>>>  drivers/mmc/host/dw_mmc.c | 14 +++++---------
>>>>>  1 file changed, 5 insertions(+), 9 deletions(-)
>>>>>
>>>>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>>>>> index a9ac0b4573131..3d62b0a1f81cb 100644
>>>>> --- a/drivers/mmc/host/dw_mmc.c
>>>>> +++ b/drivers/mmc/host/dw_mmc.c
>>>>> @@ -2968,10 +2968,8 @@ static struct dw_mci_board *dw_mci_parse_dt(struct dw_mci *host)
>>>>>  
>>>>>  	/* find reset controller when exist */
>>>>>  	pdata->rstc = devm_reset_control_get_optional(dev, "reset");
>>>>> -	if (IS_ERR(pdata->rstc)) {
>>>>> -		if (PTR_ERR(pdata->rstc) == -EPROBE_DEFER)
>>>>> -			return ERR_PTR(-EPROBE_DEFER);
>>>>> -	}
>>>>> +	if (IS_ERR(pdata->rstc))
>>>>> +		return ERR_CAST(pdata->rstc);
>>>> With three lines above commented out it works.
>>> So devm_reset_control_get_optional returns -EINVAL. Why?
>>>
>>> The mshc@...60000 node is compatible to "samsung,exynos7-dw-mshc-smu",
>>> so that's dw_mmc-exynos.c calling dw_mci_pltfm_register, which then
>>> calls dw_mci_probe, passing the original platform device as
>>> host->dev = &pdev->dev, and I expect __of_reset_control_get being called
>>> with a valid DT node (dev->of_node).
>>> Since id is set to "reset", of_property_match_string(node,
>>> "reset-names", id) should then be called and return -EINVAL because the
>>> "reset-names" property does not exist. Then __of_reset_control_get
>>> should return NULL because optional == true.
>>> Some of this obviously doesn't happen, where am I wrong?
>>
>> When RESET_CONTROLLER is not enabled dummy stubs return -ENOSUPP error [1].
>>
>> [1]: http://lxr.free-electrons.com/source/include/linux/reset.h#L77
> Thanks, I suppose that issue should be fixed by:
>
> ----------8<----------
> diff --git a/include/linux/reset.h b/include/linux/reset.h
> index 86b4ed75359e8..c905ff1c21ec6 100644
> --- a/include/linux/reset.h
> +++ b/include/linux/reset.h
> @@ -74,14 +74,14 @@ static inline struct reset_control *__of_reset_control_get(
>  					const char *id, int index, bool shared,
>  					bool optional)
>  {
> -	return ERR_PTR(-ENOTSUPP);
> +	return optional ? NULL : ERR_PTR(-ENOTSUPP);
>  }
>  
>  static inline struct reset_control *__devm_reset_control_get(
>  					struct device *dev, const char *id,
>  					int index, bool shared, bool optional)
>  {
> -	return ERR_PTR(-ENOTSUPP);
> +	return optional ? NULL : ERR_PTR(-ENOTSUPP);
>  }
>  
>  #endif /* CONFIG_RESET_CONTROLLER */
> ---------->8----------

In dw_mmc.c file there are also unconditional calls to
reset_control_assert, with disabled RESET_CONTROLLER it will cause
unexpected WARNs.
Anyway if you change reset API as above I think you should remove all
warns from reset stubs, because NULL reset is valid, but these warns are
there for reason - contradiction.

Regards
Andrzej

>
> regards
> Philipp
>
>
>
>