[PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Javier Martinez Canillas]

The operation conditions register (OCR) stores the voltage
profile of the card, however the list of possible voltages
is restricted by the voltage range supported by the supply
used as VCC/VDD. So in mmc_vddrange_to_ocrmask() a OCR mask
is obtained to filter the not supported voltages, from the
value read in the host controller OCR register.

For fixed regulators, regulator_list_voltage() returns the
fixed output for the first selector but this doesn't happen
for switch (FET) regulators that obtain their voltage from
their parent supply. A call to regulator_get_voltage() is
needed in this case so the regulator core can return the
FET's parent supply voltage output.

This change is consistent with the fact that for other
fixed regulators (that are not FETs) the OCR mask is
returned even when mmc_regulator_set_ocr() checks if the
regulator is fixed before calling regulator_set_voltage().

Without this patch, the following warning is reported when
a FET is used as a vmmc-supply:

dwmmc_exynos 12220000.mmc: Failed getting OCR mask: -22

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
---

 drivers/mmc/core/core.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 7dc0c85..8abae04 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1221,15 +1221,14 @@ int mmc_regulator_get_ocrmask(struct regulator *supply)
 	int			result = 0;
 	int			count;
 	int			i;
+	int			vdd_uV;
+	int			vdd_mV;
 
 	count = regulator_count_voltages(supply);
 	if (count < 0)
 		return count;
 
 	for (i = 0; i < count; i++) {
-		int		vdd_uV;
-		int		vdd_mV;
-
 		vdd_uV = regulator_list_voltage(supply, i);
 		if (vdd_uV <= 0)
 			continue;
@@ -1238,6 +1237,15 @@ int mmc_regulator_get_ocrmask(struct regulator *supply)
 		result |= mmc_vddrange_to_ocrmask(vdd_mV, vdd_mV);
 	}
 
+	if (!result) {
+		vdd_uV = regulator_get_voltage(supply);
+		if (vdd_uV <= 0)
+			return vdd_uV;
+
+		vdd_mV = vdd_uV / 1000;
+		result = mmc_vddrange_to_ocrmask(vdd_mV, vdd_mV);
+	}
+
 	return result;
 }
 EXPORT_SYMBOL_GPL(mmc_regulator_get_ocrmask);
-- 
2.0.0.rc2

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Tim Kryger]

On Thu, Aug 14, 2014 at 5:39 AM, Javier Martinez Canillas
<javier.martinez@collabora.co.uk> wrote:
> The operation conditions register (OCR) stores the voltage
> profile of the card, however the list of possible voltages
> is restricted by the voltage range supported by the supply
> used as VCC/VDD. So in mmc_vddrange_to_ocrmask() a OCR mask
> is obtained to filter the not supported voltages, from the
> value read in the host controller OCR register.
>
> For fixed regulators, regulator_list_voltage() returns the
> fixed output for the first selector but this doesn't happen
> for switch (FET) regulators that obtain their voltage from
> their parent supply. A call to regulator_get_voltage() is
> needed in this case so the regulator core can return the
> FET's parent supply voltage output.
>
> This change is consistent with the fact that for other
> fixed regulators (that are not FETs) the OCR mask is
> returned even when mmc_regulator_set_ocr() checks if the
> regulator is fixed before calling regulator_set_voltage().
>
> Without this patch, the following warning is reported when
> a FET is used as a vmmc-supply:
>
> dwmmc_exynos 12220000.mmc: Failed getting OCR mask: -22
>
> Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>

https://lkml.org/lkml/2014/8/12/377

Perhaps I misunderstood the discussion in that thread but couldn't
this failure also be addressed by adding proper constraints for each
FET in individual DTS files to reflect the range of voltages that are
safe for all consumers of that supply on the board?

I thought the main concern with your other change was that the
constraints you listed in the DTSI represented the limits of the PMIC
and not the consumers.

-Tim

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Mark Brown]

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On Thu, Aug 14, 2014 at 07:13:00AM -0700, Tim Kryger wrote:
> On Thu, Aug 14, 2014 at 5:39 AM, Javier Martinez Canillas

> > Without this patch, the following warning is reported when
> > a FET is used as a vmmc-supply:

> > dwmmc_exynos 12220000.mmc: Failed getting OCR mask: -22

> > Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>

> https://lkml.org/lkml/2014/8/12/377

For the benefit of those reading here 

> Perhaps I misunderstood the discussion in that thread but couldn't
> this failure also be addressed by adding proper constraints for each
> FET in individual DTS files to reflect the range of voltages that are
> safe for all consumers of that supply on the board?

> I thought the main concern with your other change was that the
> constraints you listed in the DTSI represented the limits of the PMIC
> and not the consumers.

Right, there's two things going on here.  One is that as you describe we
shouldn't be putting constraints in .dtsi files if we don't know they're
OK for a given board.  The other thing is that on this particular board
it turns out that there's no support for varying the voltages at all so
it doesn't make sense to have to specify a range, there's only one value
anyway so the software really should be able to figure out that fixed
value all by itself.

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Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Javier Martinez Canillas]

Hello Tim,

Thanks for your feedback.

On 08/14/2014 04:13 PM, Tim Kryger wrote:
> 
> https://lkml.org/lkml/2014/8/12/377
> 
> Perhaps I misunderstood the discussion in that thread but couldn't
> this failure also be addressed by adding proper constraints for each
> FET in individual DTS files to reflect the range of voltages that are
> safe for all consumers of that supply on the board?
> 
> I thought the main concern with your other change was that the
> constraints you listed in the DTSI represented the limits of the PMIC
> and not the consumers.
> 
> -Tim
> 

Yes, if the child regulator has the constraints defined then
regulator_voltage_list() won't filter the obtained parent voltage so it
won't be necessary to call regulator_get_voltage() directly.

But as Mark said on the thread you referred [0], if the voltage is not
allowed to change for a regulator then it makes no sense to have their
constraints specify a voltage range. And in this particular case the
parent supply of the FET used as vmmc-supply is a fixed regulator.

Now I wonder why mmc_regulator_get_ocrmask() even sets as a valid voltage
in the OCR mask the voltage for a fixed regulator if
mmc_regulator_set_ocr() is a no-op in this case but I guess is because
users of this function shouldn't really care about this peculiarity. In
any case, this change is consistent since with this patch FETs behaves the
same as other fixed regulators whose voltage can't be changed but the
voltage is still reported in the OCR mask.

Best regards,
Javier

[0]: https://lkml.org/lkml/2014/8/13/364

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Tim Kryger]

On Thu, Aug 14, 2014 at 8:19 AM, Mark Brown <broonie@kernel.org> wrote:

> Right, there's two things going on here.  One is that as you describe we
> shouldn't be putting constraints in .dtsi files if we don't know they're
> OK for a given board.  The other thing is that on this particular board
> it turns out that there's no support for varying the voltages at all so
> it doesn't make sense to have to specify a range, there's only one value
> anyway so the software really should be able to figure out that fixed
> value all by itself.

If constraints are truly irrelevant when the voltage supplied to
consumers is fixed, why doesn't regulator_list_voltage honor this
exemption and skip the voltage filtering that uses (potentially
unspecified) constraints when output is entirely determined by a
parent (or grandparent) supply that can't change its voltage?

It seems odd to make callers be the ones to handle this subtlety.

Thanks,
Tim Kryger

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Javier Martinez Canillas]

Hello Tim,

On 08/15/2014 07:36 AM, Tim Kryger wrote:
> On Thu, Aug 14, 2014 at 8:19 AM, Mark Brown <broonie@kernel.org> wrote:
> 
>> Right, there's two things going on here.  One is that as you describe we
>> shouldn't be putting constraints in .dtsi files if we don't know they're
>> OK for a given board.  The other thing is that on this particular board
>> it turns out that there's no support for varying the voltages at all so
>> it doesn't make sense to have to specify a range, there's only one value
>> anyway so the software really should be able to figure out that fixed
>> value all by itself.
> 
> If constraints are truly irrelevant when the voltage supplied to
> consumers is fixed, why doesn't regulator_list_voltage honor this
> exemption and skip the voltage filtering that uses (potentially
> unspecified) constraints when output is entirely determined by a
> parent (or grandparent) supply that can't change its voltage?
>

I had a similar thought before and proposed the patch:

"[RFC 3/5] regulator: core: Only apply constraints if available on list
voltage" [0].

But then Mark explained to me that this is wrong since in that case
regulator_list_voltage() will list voltages that can't really be set [1].

But now I wonder why regulator_list_voltage() even list the voltage for
fixed regulators (desc->fixed_uV) since they don't have the ability to
vary voltage. The regulator_list_voltage() documentation says:

"Returns a voltage that can be passed to @regulator_set_voltage(), zero if
this selector code can't be used on this system, or a negative errno."

But in the case of fixed regulators, it is actually listing a voltage that
can't be selected. Although regulator_set_voltage() checks if the desired
voltage is equal to the regulator min_uV and max_uV and just exits in that
case, it feels wrong to list the voltage for a fixed regulators.

regulator_list_voltage() only works because of the way we define the
generic fixed voltage regulators and that is assuming that
"regulator-min-microvolt" and "regulator-max-microvolt" DT properties
being the same means that the regulator is fixed.

This is kind of unfortunate, maybe it would had been better to define it
explicitly using a "regulator-fixed-microvolt" or something. If we had
such a DT property, then constraints wouldn't had been set for fixed
regulators and regulator_list_voltage() wouldn't list its voltage neither.

> It seems odd to make callers be the ones to handle this subtlety.
> 

If regulator_list_voltage() didn't list the voltage for fixed regulators,
then this subtlety should had been handled by callers before but they
didn't because they rely on regulator_list_voltage() to always return a
voltage even for fixed regulators.

> Thanks,
> Tim Kryger
> 

Best regards,
Javier

[0]: https://lkml.org/lkml/2014/7/29/418
[1]: https://lkml.org/lkml/2014/7/29/453

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Mark Brown]

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On Thu, Aug 14, 2014 at 10:36:18PM -0700, Tim Kryger wrote:
> On Thu, Aug 14, 2014 at 8:19 AM, Mark Brown <broonie@kernel.org> wrote:
> 
> > Right, there's two things going on here.  One is that as you describe we
> > shouldn't be putting constraints in .dtsi files if we don't know they're
> > OK for a given board.  The other thing is that on this particular board
> > it turns out that there's no support for varying the voltages at all so
> > it doesn't make sense to have to specify a range, there's only one value
> > anyway so the software really should be able to figure out that fixed
> > value all by itself.

> If constraints are truly irrelevant when the voltage supplied to
> consumers is fixed, why doesn't regulator_list_voltage honor this
> exemption and skip the voltage filtering that uses (potentially
> unspecified) constraints when output is entirely determined by a
> parent (or grandparent) supply that can't change its voltage?

> It seems odd to make callers be the ones to handle this subtlety.

regulator_list_voltage() tells the consumer what voltages could be set,
regulator_get_voltage() tells the consumer what the voltage currently
is.  These aren't quite the same thing.

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Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Mark Brown]

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On Fri, Aug 15, 2014 at 09:48:43AM +0200, Javier Martinez Canillas wrote:

> But now I wonder why regulator_list_voltage() even list the voltage for
> fixed regulators (desc->fixed_uV) since they don't have the ability to
> vary voltage. The regulator_list_voltage() documentation says:

That's because it's very cheap to do and there is a comprehensible thing
we can return - if we have to read the voltage that means potentially
asking the hardware in an I2C transaction which is not cheap.

> > It seems odd to make callers be the ones to handle this subtlety.

> If regulator_list_voltage() didn't list the voltage for fixed regulators,
> then this subtlety should had been handled by callers before but they
> didn't because they rely on regulator_list_voltage() to always return a
> voltage even for fixed regulators.

There's plenty of potentially variable regulators used in these
situations, I expect it's more likely that people were just ignoring the
warning since it has no practical effect.

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Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Javier Martinez Canillas]

Hello Mark,

On 08/15/2014 11:55 AM, Mark Brown wrote:
> On Fri, Aug 15, 2014 at 09:48:43AM +0200, Javier Martinez Canillas wrote:
> 
>> But now I wonder why regulator_list_voltage() even list the voltage for
>> fixed regulators (desc->fixed_uV) since they don't have the ability to
> 
> That's because it's very cheap to do and there is a comprehensible thing
> we can return - if we have to read the voltage that means potentially
> asking the hardware in an I2C transaction which is not cheap.
> 

Thanks a lot for the explanation, that does make a lot of sense.

> 
> There's plenty of potentially variable regulators used in these
> situations, I expect it's more likely that people were just ignoring the
> warning since it has no practical effect.
> 

Indeed.

Best regards,
Javier

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Tim Kryger]

On Fri, Aug 15, 2014 at 12:48 AM, Javier Martinez Canillas
<javier.martinez@collabora.co.uk> wrote:
> Hello Tim,
>
> On 08/15/2014 07:36 AM, Tim Kryger wrote:
>> On Thu, Aug 14, 2014 at 8:19 AM, Mark Brown <broonie@kernel.org> wrote:
>>
>>> Right, there's two things going on here.  One is that as you describe we
>>> shouldn't be putting constraints in .dtsi files if we don't know they're
>>> OK for a given board.  The other thing is that on this particular board
>>> it turns out that there's no support for varying the voltages at all so
>>> it doesn't make sense to have to specify a range, there's only one value
>>> anyway so the software really should be able to figure out that fixed
>>> value all by itself.
>>
>> If constraints are truly irrelevant when the voltage supplied to
>> consumers is fixed, why doesn't regulator_list_voltage honor this
>> exemption and skip the voltage filtering that uses (potentially
>> unspecified) constraints when output is entirely determined by a
>> parent (or grandparent) supply that can't change its voltage?
>>
>
> I had a similar thought before and proposed the patch:
>
> "[RFC 3/5] regulator: core: Only apply constraints if available on list
> voltage" [0].

> [0]: https://lkml.org/lkml/2014/7/29/418

You proposed constraints only be applied when they are defined.

That is a little different from my suggestion where the constraints
check is skipped when the regulator output is fixed.  It effectively
does this now when the regulator itself provides the fixed voltage.
However, the checks aren't skipped when that fixed voltage is coming
from an ancestor.  Why the difference?

-Tim

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Ulf Hansson]

On 15 August 2014 11:55, Mark Brown <broonie@kernel.org> wrote:
> On Fri, Aug 15, 2014 at 09:48:43AM +0200, Javier Martinez Canillas wrote:
>
>> But now I wonder why regulator_list_voltage() even list the voltage for
>> fixed regulators (desc->fixed_uV) since they don't have the ability to
>> vary voltage. The regulator_list_voltage() documentation says:
>
> That's because it's very cheap to do and there is a comprehensible thing
> we can return - if we have to read the voltage that means potentially
> asking the hardware in an I2C transaction which is not cheap.
>
>> > It seems odd to make callers be the ones to handle this subtlety.
>
>> If regulator_list_voltage() didn't list the voltage for fixed regulators,
>> then this subtlety should had been handled by callers before but they
>> didn't because they rely on regulator_list_voltage() to always return a
>> voltage even for fixed regulators.
>
> There's plenty of potentially variable regulators used in these
> situations, I expect it's more likely that people were just ignoring the
> warning since it has no practical effect.

Just wanted to add some input regarding the errors in the mmc case.
These are of high importance. In principle if you get, "Failed getting
OCR mask: -22", likely you will be using a wrong OCR mask while
negotiating the voltage level with the card.

So, somehow we need to address this issue.

Kind regards
Uffe

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Mark Brown]

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On Fri, Aug 15, 2014 at 07:19:41AM -0700, Tim Kryger wrote:

> That is a little different from my suggestion where the constraints
> check is skipped when the regulator output is fixed.  It effectively
> does this now when the regulator itself provides the fixed voltage.
> However, the checks aren't skipped when that fixed voltage is coming
> from an ancestor.  Why the difference?

Nobody has written suitable code, and please bear in mind that even if
the code is written there will probably be cases where it's too
expensive for whatever reason so Javier's change is going to be needed.

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Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Mark Brown]

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On Fri, Aug 15, 2014 at 04:51:38PM +0200, Ulf Hansson wrote:

> Just wanted to add some input regarding the errors in the mmc case.
> These are of high importance. In principle if you get, "Failed getting
> OCR mask: -22", likely you will be using a wrong OCR mask while
> negotiating the voltage level with the card.

> So, somehow we need to address this issue.

Perhaps a WARN_ON() would help here - I'd not blame users for just
ignoring the current warning?

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Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Tim Kryger]

On Fri, Aug 15, 2014 at 3:29 PM, Mark Brown <broonie@kernel.org> wrote:
> On Fri, Aug 15, 2014 at 07:19:41AM -0700, Tim Kryger wrote:
>
>> That is a little different from my suggestion where the constraints
>> check is skipped when the regulator output is fixed.  It effectively
>> does this now when the regulator itself provides the fixed voltage.
>> However, the checks aren't skipped when that fixed voltage is coming
>> from an ancestor.  Why the difference?
>
> Nobody has written suitable code, and please bear in mind that even if
> the code is written there will probably be cases where it's too
> expensive for whatever reason so Javier's change is going to be needed.

I fail to see how replicating similar logic at all current
regulator_list_voltage call sites would be any more efficient than
handling this directly in regulator core.

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Mark Brown]

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On Sun, Aug 17, 2014 at 10:11:30AM -0700, Tim Kryger wrote:
> On Fri, Aug 15, 2014 at 3:29 PM, Mark Brown <broonie@kernel.org> wrote:

> > Nobody has written suitable code, and please bear in mind that even if
> > the code is written there will probably be cases where it's too
> > expensive for whatever reason so Javier's change is going to be needed.

> I fail to see how replicating similar logic at all current
> regulator_list_voltage call sites would be any more efficient than
> handling this directly in regulator core.

If you feel like writing a helper function that would be fine but
list_voltage() can't be doing expensive talking to the hardware
operations - it needs to be something people can be comfortable calling
a lot.

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Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Javier Martinez Canillas]

Hello Ulf,

On 08/15/2014 04:51 PM, Ulf Hansson wrote:
> 
> Just wanted to add some input regarding the errors in the mmc case.
> These are of high importance. In principle if you get, "Failed getting
> OCR mask: -22", likely you will be using a wrong OCR mask while
> negotiating the voltage level with the card.
> 
> So, somehow we need to address this issue.
>

And do you think that $subject is the right approach to solve this issue?
If not please let me know so I can address that.

> Kind regards
> Uffe
> 

Best regards,
Javier

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Ulf Hansson]

On 19 August 2014 13:29, Javier Martinez Canillas
<javier.martinez@collabora.co.uk> wrote:
> Hello Ulf,
>
> On 08/15/2014 04:51 PM, Ulf Hansson wrote:
>>
>> Just wanted to add some input regarding the errors in the mmc case.
>> These are of high importance. In principle if you get, "Failed getting
>> OCR mask: -22", likely you will be using a wrong OCR mask while
>> negotiating the voltage level with the card.
>>
>> So, somehow we need to address this issue.
>>
>
> And do you think that $subject is the right approach to solve this issue?
> If not please let me know so I can address that.

Well, currently this seems like the best approach. If we end up having
some new regulator helper function, future wise, we can convert to
such later on.

Kind regards
Uffe

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Ulf Hansson]

On 14 August 2014 14:39, Javier Martinez Canillas
<javier.martinez@collabora.co.uk> wrote:
> The operation conditions register (OCR) stores the voltage
> profile of the card, however the list of possible voltages
> is restricted by the voltage range supported by the supply
> used as VCC/VDD. So in mmc_vddrange_to_ocrmask() a OCR mask
> is obtained to filter the not supported voltages, from the
> value read in the host controller OCR register.
>
> For fixed regulators, regulator_list_voltage() returns the
> fixed output for the first selector but this doesn't happen
> for switch (FET) regulators that obtain their voltage from
> their parent supply. A call to regulator_get_voltage() is
> needed in this case so the regulator core can return the
> FET's parent supply voltage output.
>
> This change is consistent with the fact that for other
> fixed regulators (that are not FETs) the OCR mask is
> returned even when mmc_regulator_set_ocr() checks if the
> regulator is fixed before calling regulator_set_voltage().
>
> Without this patch, the following warning is reported when
> a FET is used as a vmmc-supply:
>
> dwmmc_exynos 12220000.mmc: Failed getting OCR mask: -22
>
> Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>

Thanks! Applied for next.

Kind regards
Uffe

> ---
>
>  drivers/mmc/core/core.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 7dc0c85..8abae04 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1221,15 +1221,14 @@ int mmc_regulator_get_ocrmask(struct regulator *supply)
>         int                     result = 0;
>         int                     count;
>         int                     i;
> +       int                     vdd_uV;
> +       int                     vdd_mV;
>
>         count = regulator_count_voltages(supply);
>         if (count < 0)
>                 return count;
>
>         for (i = 0; i < count; i++) {
> -               int             vdd_uV;
> -               int             vdd_mV;
> -
>                 vdd_uV = regulator_list_voltage(supply, i);
>                 if (vdd_uV <= 0)
>                         continue;
> @@ -1238,6 +1237,15 @@ int mmc_regulator_get_ocrmask(struct regulator *supply)
>                 result |= mmc_vddrange_to_ocrmask(vdd_mV, vdd_mV);
>         }
>
> +       if (!result) {
> +               vdd_uV = regulator_get_voltage(supply);
> +               if (vdd_uV <= 0)
> +                       return vdd_uV;
> +
> +               vdd_mV = vdd_uV / 1000;
> +               result = mmc_vddrange_to_ocrmask(vdd_mV, vdd_mV);
> +       }
> +
>         return result;
>  }
>  EXPORT_SYMBOL_GPL(mmc_regulator_get_ocrmask);
> --
> 2.0.0.rc2
>

Re: [PATCH 1/1] mmc: core: Use regulator_get_voltage() if OCR mask is empty.

[Javier Martinez Canillas]

On 08/19/2014 02:43 PM, Ulf Hansson wrote:
> 
> Well, currently this seems like the best approach. If we end up having
> some new regulator helper function, future wise, we can convert to
> such later on.
>

Great, thanks a lot for your help!

> Kind regards
> Uffe
> 

Best regards,
Javier