[RFC 0/2] Add device tree property and quirk for supporting sdhci

[RFC 0/2] Add device tree property and quirk for supporting sdhci

[Zach Brown]

Some board configurations can not support sd highspeed mode due to the distance
between the card slot and the controller. The card and controller report that
they are capable of highspeed however, so we need a mechanism for specifying
that the setup is incapable of supporting highspeed mode.

The first patch adds documentation about a new devicetree property
sd-broken-highspeed.

The second patch keeps the sd controller and card from going into highspeed
mode when the property is set.

Chen Yee Chew (1):
  sdhci: Prevent SD from doing high-speed timing when
    sd-broken-highspeed     property is set

Zach Brown (1):
  sdhci: Add device tree property sd-broken-highspeed

 Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
 arch/arm/boot/dts/ni-77D5.dts                 | 1 -
 drivers/mmc/host/sdhci-pltfm.c                | 3 +++
 drivers/mmc/host/sdhci.c                      | 3 ++-
 drivers/mmc/host/sdhci.h                      | 2 ++
 5 files changed, 9 insertions(+), 2 deletions(-)

-- 
2.7.4

[RFC 0/2] Add device tree property and quirk for supporting sdhci

[Zach Brown]

Some board configurations can not support sd highspeed mode due to the distance
between the card slot and the controller. The card and controller report that
they are capable of highspeed however, so we need a mechanism for specifying
that the setup is incapable of supporting highspeed mode.

The first patch adds documentation about a new devicetree property
sd-broken-highspeed.

The second patch keeps the sd controller and card from going into highspeed
mode when the property is set.

Chen Yee Chew (1):
  sdhci: Prevent SD from doing high-speed timing when
    sd-broken-highspeed     property is set

Zach Brown (1):
  sdhci: Add device tree property sd-broken-highspeed

 Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
 arch/arm/boot/dts/ni-77D5.dts                 | 1 -
 drivers/mmc/host/sdhci-pltfm.c                | 3 +++
 drivers/mmc/host/sdhci.c                      | 3 ++-
 drivers/mmc/host/sdhci.h                      | 2 ++
 5 files changed, 9 insertions(+), 2 deletions(-)

-- 
2.7.4

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[RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Zach Brown]

Certain board configurations can make highspeed malfunction due to
timing issues. In these cases a way is needed to force the controller
and card into standard speed even if they otherwise appear to be capable
of highspeed.

The sd-broken-highspeed property will let the sdhci driver know that
highspeed will not work.

Signed-off-by: Zach Brown <zach.brown@ni.com>
---
 Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
index 8a37782..59332ea 100644
--- a/Documentation/devicetree/bindings/mmc/mmc.txt
+++ b/Documentation/devicetree/bindings/mmc/mmc.txt
@@ -52,6 +52,8 @@ Optional properties:
 - no-sdio: controller is limited to send sdio cmd during initialization
 - no-sd: controller is limited to send sd cmd during initialization
 - no-mmc: controller is limited to send mmc cmd during initialization
+- sd-broken-highspeed: Highspeed is broken, even if the controller and card
+  themselves claim they support highspeed.
 
 *NOTE* on CD and WP polarity. To use common for all SD/MMC host controllers line
 polarity properties, we have to fix the meaning of the "normal" and "inverted"
-- 
2.7.4

[RFC 2/2] sdhci: Prevent SD from doing highspeed timing when sd-broken-highspeed property is set

[Zach Brown]

From: Chen Yee Chew <chen.yee.chew@ni.com>

When the sd-broken-highspeed property is set the sdhci driver will not
go into highspeed mode even if the controller and card appear to
otherwise support highspeed mode.

This is useful in cases where the controller and card support highspeed,
but the board configuration or some other issue make highspeed
impossible.

Signed-off-by: Chen Yee Chew <chen.yee.chew@ni.com>
Reviewed-by: Keng Soon Cheah <keng.soon.cheah@ni.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Zach Brown <zach.brown@ni.com>
---
 drivers/mmc/host/sdhci-pltfm.c | 3 +++
 drivers/mmc/host/sdhci.c       | 3 ++-
 drivers/mmc/host/sdhci.h       | 2 ++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/host/sdhci-pltfm.c b/drivers/mmc/host/sdhci-pltfm.c
index ad49bfa..7482706 100644
--- a/drivers/mmc/host/sdhci-pltfm.c
+++ b/drivers/mmc/host/sdhci-pltfm.c
@@ -87,6 +87,9 @@ void sdhci_get_of_property(struct platform_device *pdev)
 	if (of_get_property(np, "broken-cd", NULL))
 		host->quirks |= SDHCI_QUIRK_BROKEN_CARD_DETECTION;
 
+	if (of_get_property(np, "sd-broken-highspeed", NULL))
+		host->quirks2 |= SDHCI_QUIRK2_BROKEN_HISPD;
+
 	if (of_get_property(np, "no-1-8-v", NULL))
 		host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
 
diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 4805566..4b0969c 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -3274,7 +3274,8 @@ int sdhci_setup_host(struct sdhci_host *host)
 	if (host->quirks2 & SDHCI_QUIRK2_HOST_NO_CMD23)
 		mmc->caps &= ~MMC_CAP_CMD23;
 
-	if (host->caps & SDHCI_CAN_DO_HISPD)
+	if ((host->caps & SDHCI_CAN_DO_HISPD) &&
+	    !(host->quirks2 & SDHCI_QUIRK2_BROKEN_HISPD))
 		mmc->caps |= MMC_CAP_SD_HIGHSPEED | MMC_CAP_MMC_HIGHSPEED;
 
 	if ((host->quirks & SDHCI_QUIRK_BROKEN_CARD_DETECTION) &&
diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
index c722cd2..3d0fdda 100644
--- a/drivers/mmc/host/sdhci.h
+++ b/drivers/mmc/host/sdhci.h
@@ -424,6 +424,8 @@ struct sdhci_host {
 #define SDHCI_QUIRK2_ACMD23_BROKEN			(1<<14)
 /* Broken Clock divider zero in controller */
 #define SDHCI_QUIRK2_CLOCK_DIV_ZERO_BROKEN		(1<<15)
+/* Highspeed is broken even if it appears otherwise */
+#define SDHCI_QUIRK2_BROKEN_HISPD		(1<<16)
 
 	int irq;		/* Device IRQ */
 	void __iomem *ioaddr;	/* Mapped address */
-- 
2.7.4

Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Rob Herring]

On Fri, Sep 23, 2016 at 03:01:08PM -0500, Zach Brown wrote:
> Certain board configurations can make highspeed malfunction due to
> timing issues. In these cases a way is needed to force the controller
> and card into standard speed even if they otherwise appear to be capable
> of highspeed.
> 
> The sd-broken-highspeed property will let the sdhci driver know that
> highspeed will not work.
> 
> Signed-off-by: Zach Brown <zach.brown@ni.com>
> ---
>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>  1 file changed, 2 insertions(+)

Acked-by: Rob Herring <robh@kernel.org>

Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Rob Herring]

On Fri, Sep 23, 2016 at 03:01:08PM -0500, Zach Brown wrote:
> Certain board configurations can make highspeed malfunction due to
> timing issues. In these cases a way is needed to force the controller
> and card into standard speed even if they otherwise appear to be capable
> of highspeed.
> 
> The sd-broken-highspeed property will let the sdhci driver know that
> highspeed will not work.
> 
> Signed-off-by: Zach Brown <zach.brown-acOepvfBmUk@public.gmane.org>
> ---
>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>  1 file changed, 2 insertions(+)

Acked-by: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
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Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Ulf Hansson]

On 23 September 2016 at 22:01, Zach Brown <zach.brown@ni.com> wrote:
> Certain board configurations can make highspeed malfunction due to
> timing issues. In these cases a way is needed to force the controller
> and card into standard speed even if they otherwise appear to be capable
> of highspeed.
>
> The sd-broken-highspeed property will let the sdhci driver know that
> highspeed will not work.
>
> Signed-off-by: Zach Brown <zach.brown@ni.com>
> ---
>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
> index 8a37782..59332ea 100644
> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
> @@ -52,6 +52,8 @@ Optional properties:
>  - no-sdio: controller is limited to send sdio cmd during initialization
>  - no-sd: controller is limited to send sd cmd during initialization
>  - no-mmc: controller is limited to send mmc cmd during initialization
> +- sd-broken-highspeed: Highspeed is broken, even if the controller and card
> +  themselves claim they support highspeed.

Regarding a broken card, that is managed via the card quirks and not in DT.

If this is about a controller limitation, we already have the option
to describe what it supports, so we don't need an option to tell what
it *not* supports.

For example "cap-sd-highspeed" tells whether the controller supports
SD high-speed, please use that instead.

>
>  *NOTE* on CD and WP polarity. To use common for all SD/MMC host controllers line
>  polarity properties, we have to fix the meaning of the "normal" and "inverted"
> --
> 2.7.4
>

Kind regards
Uffe

Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Rob Herring]

On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> On 23 September 2016 at 22:01, Zach Brown <zach.brown@ni.com> wrote:
>> Certain board configurations can make highspeed malfunction due to
>> timing issues. In these cases a way is needed to force the controller
>> and card into standard speed even if they otherwise appear to be capable
>> of highspeed.
>>
>> The sd-broken-highspeed property will let the sdhci driver know that
>> highspeed will not work.
>>
>> Signed-off-by: Zach Brown <zach.brown@ni.com>
>> ---
>>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
>> index 8a37782..59332ea 100644
>> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
>> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
>> @@ -52,6 +52,8 @@ Optional properties:
>>  - no-sdio: controller is limited to send sdio cmd during initialization
>>  - no-sd: controller is limited to send sd cmd during initialization
>>  - no-mmc: controller is limited to send mmc cmd during initialization
>> +- sd-broken-highspeed: Highspeed is broken, even if the controller and card
>> +  themselves claim they support highspeed.
>
> Regarding a broken card, that is managed via the card quirks and not in DT.
>
> If this is about a controller limitation, we already have the option
> to describe what it supports, so we don't need an option to tell what
> it *not* supports.
>
> For example "cap-sd-highspeed" tells whether the controller supports
> SD high-speed, please use that instead.

If a controller has a capability register and it lies (perhaps the
board has limitations that the SoC does not), then you may need to
disable a feature.

Rob

Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Julia Cartwright]

On Wed, Oct 05, 2016 at 03:03:44PM -0500, Rob Herring wrote:
> On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> > On 23 September 2016 at 22:01, Zach Brown <zach.brown@ni.com> wrote:
> >> Certain board configurations can make highspeed malfunction due to
> >> timing issues. In these cases a way is needed to force the controller
> >> and card into standard speed even if they otherwise appear to be capable
> >> of highspeed.
> >>
> >> The sd-broken-highspeed property will let the sdhci driver know that
> >> highspeed will not work.
> >>
> >> Signed-off-by: Zach Brown <zach.brown@ni.com>
> >> ---
> >>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
> >> index 8a37782..59332ea 100644
> >> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
> >> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
> >> @@ -52,6 +52,8 @@ Optional properties:
> >>  - no-sdio: controller is limited to send sdio cmd during initialization
> >>  - no-sd: controller is limited to send sd cmd during initialization
> >>  - no-mmc: controller is limited to send mmc cmd during initialization
> >> +- sd-broken-highspeed: Highspeed is broken, even if the controller and card
> >> +  themselves claim they support highspeed.
> >
> > Regarding a broken card, that is managed via the card quirks and not in DT.
> >
> > If this is about a controller limitation, we already have the option
> > to describe what it supports, so we don't need an option to tell what
> > it *not* supports.
> >
> > For example "cap-sd-highspeed" tells whether the controller supports
> > SD high-speed, please use that instead.
> 
> If a controller has a capability register and it lies (perhaps the
> board has limitations that the SoC does not), then you may need to
> disable a feature.

That's precisely the case here.  This is a board-level problem, not a
card or controller problem.  As Zach mentioned in the cover letter, the
trace length between controller and card on some of our boards is too
long to meet high-speed timings, even though both card and controller
advertise it.

Thanks,
   Julia

Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Julia Cartwright]

On Wed, Oct 05, 2016 at 03:03:44PM -0500, Rob Herring wrote:
> On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
> > On 23 September 2016 at 22:01, Zach Brown <zach.brown-acOepvfBmUk@public.gmane.org> wrote:
> >> Certain board configurations can make highspeed malfunction due to
> >> timing issues. In these cases a way is needed to force the controller
> >> and card into standard speed even if they otherwise appear to be capable
> >> of highspeed.
> >>
> >> The sd-broken-highspeed property will let the sdhci driver know that
> >> highspeed will not work.
> >>
> >> Signed-off-by: Zach Brown <zach.brown-acOepvfBmUk@public.gmane.org>
> >> ---
> >>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
> >> index 8a37782..59332ea 100644
> >> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
> >> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
> >> @@ -52,6 +52,8 @@ Optional properties:
> >>  - no-sdio: controller is limited to send sdio cmd during initialization
> >>  - no-sd: controller is limited to send sd cmd during initialization
> >>  - no-mmc: controller is limited to send mmc cmd during initialization
> >> +- sd-broken-highspeed: Highspeed is broken, even if the controller and card
> >> +  themselves claim they support highspeed.
> >
> > Regarding a broken card, that is managed via the card quirks and not in DT.
> >
> > If this is about a controller limitation, we already have the option
> > to describe what it supports, so we don't need an option to tell what
> > it *not* supports.
> >
> > For example "cap-sd-highspeed" tells whether the controller supports
> > SD high-speed, please use that instead.
> 
> If a controller has a capability register and it lies (perhaps the
> board has limitations that the SoC does not), then you may need to
> disable a feature.

That's precisely the case here.  This is a board-level problem, not a
card or controller problem.  As Zach mentioned in the cover letter, the
trace length between controller and card on some of our boards is too
long to meet high-speed timings, even though both card and controller
advertise it.

Thanks,
   Julia
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Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Shawn Lin]

On 2016/10/6 5:22, Julia Cartwright wrote:
> On Wed, Oct 05, 2016 at 03:03:44PM -0500, Rob Herring wrote:
>> On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>>> On 23 September 2016 at 22:01, Zach Brown <zach.brown@ni.com> wrote:
>>>> Certain board configurations can make highspeed malfunction due to
>>>> timing issues. In these cases a way is needed to force the controller
>>>> and card into standard speed even if they otherwise appear to be capable
>>>> of highspeed.
>>>>
>>>> The sd-broken-highspeed property will let the sdhci driver know that
>>>> highspeed will not work.
>>>>
>>>> Signed-off-by: Zach Brown <zach.brown@ni.com>
>>>> ---
>>>>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>>>>  1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
>>>> index 8a37782..59332ea 100644
>>>> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
>>>> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
>>>> @@ -52,6 +52,8 @@ Optional properties:
>>>>  - no-sdio: controller is limited to send sdio cmd during initialization
>>>>  - no-sd: controller is limited to send sd cmd during initialization
>>>>  - no-mmc: controller is limited to send mmc cmd during initialization
>>>> +- sd-broken-highspeed: Highspeed is broken, even if the controller and card
>>>> +  themselves claim they support highspeed.
>>>
>>> Regarding a broken card, that is managed via the card quirks and not in DT.
>>>
>>> If this is about a controller limitation, we already have the option
>>> to describe what it supports, so we don't need an option to tell what
>>> it *not* supports.
>>>
>>> For example "cap-sd-highspeed" tells whether the controller supports
>>> SD high-speed, please use that instead.
>>
>> If a controller has a capability register and it lies (perhaps the
>> board has limitations that the SoC does not), then you may need to
>> disable a feature.
>
> That's precisely the case here.  This is a board-level problem, not a
> card or controller problem.  As Zach mentioned in the cover letter, the
> trace length between controller and card on some of our boards is too
> long to meet high-speed timings, even though both card and controller
> advertise it.

IIRC, I saw the same problem while using sdhci to bring up a
industrial board for vehicle. The trace length is so long that
I have to limit the max-frequency to make it works properly when
running at hishspeed.

So could you try to limit the max-frequency in your DT to see
if it could work for you? I guess it should work as once reducing
the frequency, the timing per cycle will be large enough to meet
the spec. At least that helped me solve my problem.

For further consideration, I deployed a mechanism called "tuning for
non UHS or non-hs200/400" for my donwstream tree at that time. The basic
concept is to ask devices to send ext_csd(or send status for SD case) 
*repeatedly*. Some hosts, i.e. sdhci-of-arasan or dw_mmc-rockchip, can
manually set rx delay via some clock unit registers to capture the
working sample window and select the middle point of the longest good
phase region. The same for retune. But it is a little complicated, and
could only be applicable to the hosts who could adjust the rx delay
manually when claiming the caps of MMC_CAPS_CAN_TUNING_FOR_HS, whatever
the name is...

I don't know if it is worth to add this, and I don't know if it's
a legit way. Anyway, I just share my thought(experience) for you and
linux-mmc to think more about how to deal with the case you meet rather
than sacrificing the performence by removing highspeed or reducing
frequency..


>
> Thanks,
>    Julia
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>


-- 
Best Regards
Shawn Lin

Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Adrian Hunter]

On 06/10/16 04:34, Shawn Lin wrote:
> On 2016/10/6 5:22, Julia Cartwright wrote:
>> On Wed, Oct 05, 2016 at 03:03:44PM -0500, Rob Herring wrote:
>>> On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>>>> On 23 September 2016 at 22:01, Zach Brown <zach.brown@ni.com> wrote:
>>>>> Certain board configurations can make highspeed malfunction due to
>>>>> timing issues. In these cases a way is needed to force the controller
>>>>> and card into standard speed even if they otherwise appear to be capable
>>>>> of highspeed.
>>>>>
>>>>> The sd-broken-highspeed property will let the sdhci driver know that
>>>>> highspeed will not work.
>>>>>
>>>>> Signed-off-by: Zach Brown <zach.brown@ni.com>
>>>>> ---
>>>>>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>>>>>  1 file changed, 2 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> b/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> index 8a37782..59332ea 100644
>>>>> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> @@ -52,6 +52,8 @@ Optional properties:
>>>>>  - no-sdio: controller is limited to send sdio cmd during initialization
>>>>>  - no-sd: controller is limited to send sd cmd during initialization
>>>>>  - no-mmc: controller is limited to send mmc cmd during initialization
>>>>> +- sd-broken-highspeed: Highspeed is broken, even if the controller and
>>>>> card
>>>>> +  themselves claim they support highspeed.
>>>>
>>>> Regarding a broken card, that is managed via the card quirks and not in DT.
>>>>
>>>> If this is about a controller limitation, we already have the option
>>>> to describe what it supports, so we don't need an option to tell what
>>>> it *not* supports.
>>>>
>>>> For example "cap-sd-highspeed" tells whether the controller supports
>>>> SD high-speed, please use that instead.
>>>
>>> If a controller has a capability register and it lies (perhaps the
>>> board has limitations that the SoC does not), then you may need to
>>> disable a feature.
>>
>> That's precisely the case here.  This is a board-level problem, not a
>> card or controller problem.  As Zach mentioned in the cover letter, the
>> trace length between controller and card on some of our boards is too
>> long to meet high-speed timings, even though both card and controller
>> advertise it.
> 
> IIRC, I saw the same problem while using sdhci to bring up a
> industrial board for vehicle. The trace length is so long that
> I have to limit the max-frequency to make it works properly when
> running at hishspeed.
> 
> So could you try to limit the max-frequency in your DT to see
> if it could work for you? I guess it should work as once reducing
> the frequency, the timing per cycle will be large enough to meet
> the spec. At least that helped me solve my problem.
> 
> For further consideration, I deployed a mechanism called "tuning for
> non UHS or non-hs200/400" for my donwstream tree at that time. The basic
> concept is to ask devices to send ext_csd(or send status for SD case)
> *repeatedly*. Some hosts, i.e. sdhci-of-arasan or dw_mmc-rockchip, can
> manually set rx delay via some clock unit registers to capture the
> working sample window and select the middle point of the longest good
> phase region. The same for retune. But it is a little complicated, and
> could only be applicable to the hosts who could adjust the rx delay
> manually when claiming the caps of MMC_CAPS_CAN_TUNING_FOR_HS, whatever
> the name is...
> 
> I don't know if it is worth to add this, and I don't know if it's
> a legit way. Anyway, I just share my thought(experience) for you and
> linux-mmc to think more about how to deal with the case you meet rather
> than sacrificing the performence by removing highspeed or reducing
> frequency..
> 

As Shawn points out, using max-frequency is a possibility. Did you consider
that?

There are 2 high speed caps:
	cap-sd-highspeed
	cap-mmc-highspeed

Yet patch in 2, the effect of sd-broken-highspeed is to suppress highspeed
for both SD and MMC.  Should it then be called just broken-highspeed?

Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Adrian Hunter]

On 06/10/16 04:34, Shawn Lin wrote:
> On 2016/10/6 5:22, Julia Cartwright wrote:
>> On Wed, Oct 05, 2016 at 03:03:44PM -0500, Rob Herring wrote:
>>> On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
>>>> On 23 September 2016 at 22:01, Zach Brown <zach.brown-acOepvfBmUk@public.gmane.org> wrote:
>>>>> Certain board configurations can make highspeed malfunction due to
>>>>> timing issues. In these cases a way is needed to force the controller
>>>>> and card into standard speed even if they otherwise appear to be capable
>>>>> of highspeed.
>>>>>
>>>>> The sd-broken-highspeed property will let the sdhci driver know that
>>>>> highspeed will not work.
>>>>>
>>>>> Signed-off-by: Zach Brown <zach.brown-acOepvfBmUk@public.gmane.org>
>>>>> ---
>>>>>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>>>>>  1 file changed, 2 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> b/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> index 8a37782..59332ea 100644
>>>>> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> @@ -52,6 +52,8 @@ Optional properties:
>>>>>  - no-sdio: controller is limited to send sdio cmd during initialization
>>>>>  - no-sd: controller is limited to send sd cmd during initialization
>>>>>  - no-mmc: controller is limited to send mmc cmd during initialization
>>>>> +- sd-broken-highspeed: Highspeed is broken, even if the controller and
>>>>> card
>>>>> +  themselves claim they support highspeed.
>>>>
>>>> Regarding a broken card, that is managed via the card quirks and not in DT.
>>>>
>>>> If this is about a controller limitation, we already have the option
>>>> to describe what it supports, so we don't need an option to tell what
>>>> it *not* supports.
>>>>
>>>> For example "cap-sd-highspeed" tells whether the controller supports
>>>> SD high-speed, please use that instead.
>>>
>>> If a controller has a capability register and it lies (perhaps the
>>> board has limitations that the SoC does not), then you may need to
>>> disable a feature.
>>
>> That's precisely the case here.  This is a board-level problem, not a
>> card or controller problem.  As Zach mentioned in the cover letter, the
>> trace length between controller and card on some of our boards is too
>> long to meet high-speed timings, even though both card and controller
>> advertise it.
> 
> IIRC, I saw the same problem while using sdhci to bring up a
> industrial board for vehicle. The trace length is so long that
> I have to limit the max-frequency to make it works properly when
> running at hishspeed.
> 
> So could you try to limit the max-frequency in your DT to see
> if it could work for you? I guess it should work as once reducing
> the frequency, the timing per cycle will be large enough to meet
> the spec. At least that helped me solve my problem.
> 
> For further consideration, I deployed a mechanism called "tuning for
> non UHS or non-hs200/400" for my donwstream tree at that time. The basic
> concept is to ask devices to send ext_csd(or send status for SD case)
> *repeatedly*. Some hosts, i.e. sdhci-of-arasan or dw_mmc-rockchip, can
> manually set rx delay via some clock unit registers to capture the
> working sample window and select the middle point of the longest good
> phase region. The same for retune. But it is a little complicated, and
> could only be applicable to the hosts who could adjust the rx delay
> manually when claiming the caps of MMC_CAPS_CAN_TUNING_FOR_HS, whatever
> the name is...
> 
> I don't know if it is worth to add this, and I don't know if it's
> a legit way. Anyway, I just share my thought(experience) for you and
> linux-mmc to think more about how to deal with the case you meet rather
> than sacrificing the performence by removing highspeed or reducing
> frequency..
> 

As Shawn points out, using max-frequency is a possibility. Did you consider
that?

There are 2 high speed caps:
	cap-sd-highspeed
	cap-mmc-highspeed

Yet patch in 2, the effect of sd-broken-highspeed is to suppress highspeed
for both SD and MMC.  Should it then be called just broken-highspeed?

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Re: [RFC 2/2] sdhci: Prevent SD from doing highspeed timing when sd-broken-highspeed property is set

[Adrian Hunter]

On 23/09/16 23:01, Zach Brown wrote:
> From: Chen Yee Chew <chen.yee.chew@ni.com>
> 
> When the sd-broken-highspeed property is set the sdhci driver will not
> go into highspeed mode even if the controller and card appear to
> otherwise support highspeed mode.
> 
> This is useful in cases where the controller and card support highspeed,
> but the board configuration or some other issue make highspeed
> impossible.
> 
> Signed-off-by: Chen Yee Chew <chen.yee.chew@ni.com>
> Reviewed-by: Keng Soon Cheah <keng.soon.cheah@ni.com>
> Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
> Signed-off-by: Zach Brown <zach.brown@ni.com>
> ---
>  drivers/mmc/host/sdhci-pltfm.c | 3 +++
>  drivers/mmc/host/sdhci.c       | 3 ++-
>  drivers/mmc/host/sdhci.h       | 2 ++
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/sdhci-pltfm.c b/drivers/mmc/host/sdhci-pltfm.c
> index ad49bfa..7482706 100644
> --- a/drivers/mmc/host/sdhci-pltfm.c
> +++ b/drivers/mmc/host/sdhci-pltfm.c
> @@ -87,6 +87,9 @@ void sdhci_get_of_property(struct platform_device *pdev)
>  	if (of_get_property(np, "broken-cd", NULL))
>  		host->quirks |= SDHCI_QUIRK_BROKEN_CARD_DETECTION;
>  
> +	if (of_get_property(np, "sd-broken-highspeed", NULL))
> +		host->quirks2 |= SDHCI_QUIRK2_BROKEN_HISPD;
> +

We don't really want new quirks.

>  	if (of_get_property(np, "no-1-8-v", NULL))
>  		host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
>  
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 4805566..4b0969c 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -3274,7 +3274,8 @@ int sdhci_setup_host(struct sdhci_host *host)
>  	if (host->quirks2 & SDHCI_QUIRK2_HOST_NO_CMD23)
>  		mmc->caps &= ~MMC_CAP_CMD23;
>  
> -	if (host->caps & SDHCI_CAN_DO_HISPD)
> +	if ((host->caps & SDHCI_CAN_DO_HISPD) &&
> +	    !(host->quirks2 & SDHCI_QUIRK2_BROKEN_HISPD))

Is there any reason this can't just be:

	if ((host->caps & SDHCI_CAN_DO_HISPD) &&
	    !(of_property_read_bool(mmc_dev(mmc)->of_node, "broken-highspeed")))

AFAICT it does the right thing whether or not OF is configured or of_node is null.

>  		mmc->caps |= MMC_CAP_SD_HIGHSPEED | MMC_CAP_MMC_HIGHSPEED;
>  
>  	if ((host->quirks & SDHCI_QUIRK_BROKEN_CARD_DETECTION) &&
> diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
> index c722cd2..3d0fdda 100644
> --- a/drivers/mmc/host/sdhci.h
> +++ b/drivers/mmc/host/sdhci.h
> @@ -424,6 +424,8 @@ struct sdhci_host {
>  #define SDHCI_QUIRK2_ACMD23_BROKEN			(1<<14)
>  /* Broken Clock divider zero in controller */
>  #define SDHCI_QUIRK2_CLOCK_DIV_ZERO_BROKEN		(1<<15)
> +/* Highspeed is broken even if it appears otherwise */
> +#define SDHCI_QUIRK2_BROKEN_HISPD		(1<<16)
>  
>  	int irq;		/* Device IRQ */
>  	void __iomem *ioaddr;	/* Mapped address */
> 

Re: [RFC 2/2] sdhci: Prevent SD from doing highspeed timing when sd-broken-highspeed property is set

[Adrian Hunter]

On 23/09/16 23:01, Zach Brown wrote:
> From: Chen Yee Chew <chen.yee.chew-acOepvfBmUk@public.gmane.org>
> 
> When the sd-broken-highspeed property is set the sdhci driver will not
> go into highspeed mode even if the controller and card appear to
> otherwise support highspeed mode.
> 
> This is useful in cases where the controller and card support highspeed,
> but the board configuration or some other issue make highspeed
> impossible.
> 
> Signed-off-by: Chen Yee Chew <chen.yee.chew-acOepvfBmUk@public.gmane.org>
> Reviewed-by: Keng Soon Cheah <keng.soon.cheah-acOepvfBmUk@public.gmane.org>
> Reviewed-by: Joe Hershberger <joe.hershberger-acOepvfBmUk@public.gmane.org>
> Signed-off-by: Zach Brown <zach.brown-acOepvfBmUk@public.gmane.org>
> ---
>  drivers/mmc/host/sdhci-pltfm.c | 3 +++
>  drivers/mmc/host/sdhci.c       | 3 ++-
>  drivers/mmc/host/sdhci.h       | 2 ++
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/sdhci-pltfm.c b/drivers/mmc/host/sdhci-pltfm.c
> index ad49bfa..7482706 100644
> --- a/drivers/mmc/host/sdhci-pltfm.c
> +++ b/drivers/mmc/host/sdhci-pltfm.c
> @@ -87,6 +87,9 @@ void sdhci_get_of_property(struct platform_device *pdev)
>  	if (of_get_property(np, "broken-cd", NULL))
>  		host->quirks |= SDHCI_QUIRK_BROKEN_CARD_DETECTION;
>  
> +	if (of_get_property(np, "sd-broken-highspeed", NULL))
> +		host->quirks2 |= SDHCI_QUIRK2_BROKEN_HISPD;
> +

We don't really want new quirks.

>  	if (of_get_property(np, "no-1-8-v", NULL))
>  		host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
>  
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 4805566..4b0969c 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -3274,7 +3274,8 @@ int sdhci_setup_host(struct sdhci_host *host)
>  	if (host->quirks2 & SDHCI_QUIRK2_HOST_NO_CMD23)
>  		mmc->caps &= ~MMC_CAP_CMD23;
>  
> -	if (host->caps & SDHCI_CAN_DO_HISPD)
> +	if ((host->caps & SDHCI_CAN_DO_HISPD) &&
> +	    !(host->quirks2 & SDHCI_QUIRK2_BROKEN_HISPD))

Is there any reason this can't just be:

	if ((host->caps & SDHCI_CAN_DO_HISPD) &&
	    !(of_property_read_bool(mmc_dev(mmc)->of_node, "broken-highspeed")))

AFAICT it does the right thing whether or not OF is configured or of_node is null.

>  		mmc->caps |= MMC_CAP_SD_HIGHSPEED | MMC_CAP_MMC_HIGHSPEED;
>  
>  	if ((host->quirks & SDHCI_QUIRK_BROKEN_CARD_DETECTION) &&
> diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
> index c722cd2..3d0fdda 100644
> --- a/drivers/mmc/host/sdhci.h
> +++ b/drivers/mmc/host/sdhci.h
> @@ -424,6 +424,8 @@ struct sdhci_host {
>  #define SDHCI_QUIRK2_ACMD23_BROKEN			(1<<14)
>  /* Broken Clock divider zero in controller */
>  #define SDHCI_QUIRK2_CLOCK_DIV_ZERO_BROKEN		(1<<15)
> +/* Highspeed is broken even if it appears otherwise */
> +#define SDHCI_QUIRK2_BROKEN_HISPD		(1<<16)
>  
>  	int irq;		/* Device IRQ */
>  	void __iomem *ioaddr;	/* Mapped address */
> 

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Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Ulf Hansson]

On 5 October 2016 at 22:03, Rob Herring <robh+dt@kernel.org> wrote:
> On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>> On 23 September 2016 at 22:01, Zach Brown <zach.brown@ni.com> wrote:
>>> Certain board configurations can make highspeed malfunction due to
>>> timing issues. In these cases a way is needed to force the controller
>>> and card into standard speed even if they otherwise appear to be capable
>>> of highspeed.
>>>
>>> The sd-broken-highspeed property will let the sdhci driver know that
>>> highspeed will not work.
>>>
>>> Signed-off-by: Zach Brown <zach.brown@ni.com>
>>> ---
>>>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
>>> index 8a37782..59332ea 100644
>>> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
>>> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
>>> @@ -52,6 +52,8 @@ Optional properties:
>>>  - no-sdio: controller is limited to send sdio cmd during initialization
>>>  - no-sd: controller is limited to send sd cmd during initialization
>>>  - no-mmc: controller is limited to send mmc cmd during initialization
>>> +- sd-broken-highspeed: Highspeed is broken, even if the controller and card
>>> +  themselves claim they support highspeed.
>>
>> Regarding a broken card, that is managed via the card quirks and not in DT.
>>
>> If this is about a controller limitation, we already have the option
>> to describe what it supports, so we don't need an option to tell what
>> it *not* supports.
>>
>> For example "cap-sd-highspeed" tells whether the controller supports
>> SD high-speed, please use that instead.
>
> If a controller has a capability register and it lies (perhaps the
> board has limitations that the SoC does not), then you may need to
> disable a feature.

I understand, although the SDHCI capabilities register is broken for
most SDHCI variants. In principle, we would more or less have to add a
*-broken binding for each bit in that register. I don't like that!

Maybe a better option is to add a "sdhci-cap-broken" or perhaps
"sdhci-cap-speed-modes-broken", which tells the driver to not rely on
the capabilities register and instead find out what *is* supported by
looking at the other mmc generic DT bindings.

What do you think of that?

Kind regards
Uffe

Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Ulf Hansson]

On 5 October 2016 at 22:03, Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
>> On 23 September 2016 at 22:01, Zach Brown <zach.brown-acOepvfBmUk@public.gmane.org> wrote:
>>> Certain board configurations can make highspeed malfunction due to
>>> timing issues. In these cases a way is needed to force the controller
>>> and card into standard speed even if they otherwise appear to be capable
>>> of highspeed.
>>>
>>> The sd-broken-highspeed property will let the sdhci driver know that
>>> highspeed will not work.
>>>
>>> Signed-off-by: Zach Brown <zach.brown-acOepvfBmUk@public.gmane.org>
>>> ---
>>>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
>>> index 8a37782..59332ea 100644
>>> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
>>> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
>>> @@ -52,6 +52,8 @@ Optional properties:
>>>  - no-sdio: controller is limited to send sdio cmd during initialization
>>>  - no-sd: controller is limited to send sd cmd during initialization
>>>  - no-mmc: controller is limited to send mmc cmd during initialization
>>> +- sd-broken-highspeed: Highspeed is broken, even if the controller and card
>>> +  themselves claim they support highspeed.
>>
>> Regarding a broken card, that is managed via the card quirks and not in DT.
>>
>> If this is about a controller limitation, we already have the option
>> to describe what it supports, so we don't need an option to tell what
>> it *not* supports.
>>
>> For example "cap-sd-highspeed" tells whether the controller supports
>> SD high-speed, please use that instead.
>
> If a controller has a capability register and it lies (perhaps the
> board has limitations that the SoC does not), then you may need to
> disable a feature.

I understand, although the SDHCI capabilities register is broken for
most SDHCI variants. In principle, we would more or less have to add a
*-broken binding for each bit in that register. I don't like that!

Maybe a better option is to add a "sdhci-cap-broken" or perhaps
"sdhci-cap-speed-modes-broken", which tells the driver to not rely on
the capabilities register and instead find out what *is* supported by
looking at the other mmc generic DT bindings.

What do you think of that?

Kind regards
Uffe
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Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Zach Brown]

On Thu, Oct 06, 2016 at 09:13:24AM +0300, Adrian Hunter wrote:
> On 06/10/16 04:34, Shawn Lin wrote:
> > On 2016/10/6 5:22, Julia Cartwright wrote:
> >> On Wed, Oct 05, 2016 at 03:03:44PM -0500, Rob Herring wrote:
> >>> On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> >>>> On 23 September 2016 at 22:01, Zach Brown <zach.brown@ni.com> wrote:
> >>>>> Certain board configurations can make highspeed malfunction due to
> >>>>> timing issues. In these cases a way is needed to force the controller
> >>>>> and card into standard speed even if they otherwise appear to be capable
> >>>>> of highspeed.
> >>>>>
> >>>>> The sd-broken-highspeed property will let the sdhci driver know that
> >>>>> highspeed will not work.
> >>>>>
> >>>>> Signed-off-by: Zach Brown <zach.brown@ni.com>
> >>>>> ---
> >>>>>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
> >>>>>  1 file changed, 2 insertions(+)
> >>>>>
> >>>>> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt
> >>>>> b/Documentation/devicetree/bindings/mmc/mmc.txt
> >>>>> index 8a37782..59332ea 100644
> >>>>> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
> >>>>> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
> >>>>> @@ -52,6 +52,8 @@ Optional properties:
> >>>>>  - no-sdio: controller is limited to send sdio cmd during initialization
> >>>>>  - no-sd: controller is limited to send sd cmd during initialization
> >>>>>  - no-mmc: controller is limited to send mmc cmd during initialization
> >>>>> +- sd-broken-highspeed: Highspeed is broken, even if the controller and
> >>>>> card
> >>>>> +  themselves claim they support highspeed.
> >>>>
> >>>> Regarding a broken card, that is managed via the card quirks and not in DT.
> >>>>
> >>>> If this is about a controller limitation, we already have the option
> >>>> to describe what it supports, so we don't need an option to tell what
> >>>> it *not* supports.
> >>>>
> >>>> For example "cap-sd-highspeed" tells whether the controller supports
> >>>> SD high-speed, please use that instead.
> >>>
> >>> If a controller has a capability register and it lies (perhaps the
> >>> board has limitations that the SoC does not), then you may need to
> >>> disable a feature.
> >>
> >> That's precisely the case here.  This is a board-level problem, not a
> >> card or controller problem.  As Zach mentioned in the cover letter, the
> >> trace length between controller and card on some of our boards is too
> >> long to meet high-speed timings, even though both card and controller
> >> advertise it.
> >
> > IIRC, I saw the same problem while using sdhci to bring up a
> > industrial board for vehicle. The trace length is so long that
> > I have to limit the max-frequency to make it works properly when
> > running at hishspeed.
> >
> > So could you try to limit the max-frequency in your DT to see
> > if it could work for you? I guess it should work as once reducing
> > the frequency, the timing per cycle will be large enough to meet
> > the spec. At least that helped me solve my problem.
> >
> > For further consideration, I deployed a mechanism called "tuning for
> > non UHS or non-hs200/400" for my donwstream tree at that time. The basic
> > concept is to ask devices to send ext_csd(or send status for SD case)
> > *repeatedly*. Some hosts, i.e. sdhci-of-arasan or dw_mmc-rockchip, can
> > manually set rx delay via some clock unit registers to capture the
> > working sample window and select the middle point of the longest good
> > phase region. The same for retune. But it is a little complicated, and
> > could only be applicable to the hosts who could adjust the rx delay
> > manually when claiming the caps of MMC_CAPS_CAN_TUNING_FOR_HS, whatever
> > the name is...
> >
> > I don't know if it is worth to add this, and I don't know if it's
> > a legit way. Anyway, I just share my thought(experience) for you and
> > linux-mmc to think more about how to deal with the case you meet rather
> > than sacrificing the performence by removing highspeed or reducing
> > frequency..
> >
>
> As Shawn points out, using max-frequency is a possibility. Did you consider
> that?
>

I hadn't. So I looked into it and, as I stated the issue using max-frequency
would work, but I forgot to add that, because we pass the signal through an
fpga it has to be standard speed. If the card and controller are not in
standard speed then it won't pass hold time. Specifically we need the data to
change on the falling edge of the clock.

I'll add this justification to the commit message.

> There are 2 high speed caps:
> 	cap-sd-highspeed
> 	cap-mmc-highspeed
>
> Yet patch in 2, the effect of sd-broken-highspeed is to suppress highspeed
> for both SD and MMC.  Should it then be called just broken-highspeed?
>

I agree, broken-highspeed makes more sense. Will change in the next version.

Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

[Zach Brown]

On Thu, Oct 06, 2016 at 10:03:56AM +0200, Ulf Hansson wrote:
> On 5 October 2016 at 22:03, Rob Herring <robh+dt@kernel.org> wrote:
> > On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> >> On 23 September 2016 at 22:01, Zach Brown <zach.brown@ni.com> wrote:
> >>> Certain board configurations can make highspeed malfunction due to
> >>> timing issues. In these cases a way is needed to force the controller
> >>> and card into standard speed even if they otherwise appear to be capable
> >>> of highspeed.
> >>>
> >>> The sd-broken-highspeed property will let the sdhci driver know that
> >>> highspeed will not work.
> >>>
> >>> Signed-off-by: Zach Brown <zach.brown@ni.com>
> >>> ---
> >>>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
> >>>  1 file changed, 2 insertions(+)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
> >>> index 8a37782..59332ea 100644
> >>> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
> >>> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
> >>> @@ -52,6 +52,8 @@ Optional properties:
> >>>  - no-sdio: controller is limited to send sdio cmd during initialization
> >>>  - no-sd: controller is limited to send sd cmd during initialization
> >>>  - no-mmc: controller is limited to send mmc cmd during initialization
> >>> +- sd-broken-highspeed: Highspeed is broken, even if the controller and card
> >>> +  themselves claim they support highspeed.
> >>
> >> Regarding a broken card, that is managed via the card quirks and not in DT.
> >>
> >> If this is about a controller limitation, we already have the option
> >> to describe what it supports, so we don't need an option to tell what
> >> it *not* supports.
> >>
> >> For example "cap-sd-highspeed" tells whether the controller supports
> >> SD high-speed, please use that instead.
> >
> > If a controller has a capability register and it lies (perhaps the
> > board has limitations that the SoC does not), then you may need to
> > disable a feature.
>
> I understand, although the SDHCI capabilities register is broken for
> most SDHCI variants. In principle, we would more or less have to add a
> *-broken binding for each bit in that register. I don't like that!
>
> Maybe a better option is to add a "sdhci-cap-broken" or perhaps
> "sdhci-cap-speed-modes-broken", which tells the driver to not rely on
> the capabilities register and instead find out what *is* supported by
> looking at the other mmc generic DT bindings.
>
> What do you think of that?
>
> Kind regards
> Uffe

"sdhci-cap-broken" seems too aggressive. There might only be one capability
that the register incorrectly advertises.

"sdhci-cap-speed-modes-broken" makes more sense and I will re-create this patch
set using that idea.