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

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Date:   Mon, 20 Mar 2017 11:27:59 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Andrzej Hajda <a.hajda@...sung.com>
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

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----------

regards
Philipp