[RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[Ben Chuang]

From: AKASHI Takahiro <takahiro.akashi@linaro.org>

sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
and not for UHS-II mode.

Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
---
 drivers/mmc/host/sdhci.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 5511649946b9..7f2537648a08 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
 	/*
 	 * Signal Voltage Switching is only applicable for Host Controllers
 	 * v3.00 and above.
+	 * But for UHS2, the signal voltage is supplied by vdd2 which is
+	 * already 1.8v so no voltage switch required.
 	 */
-	if (host->version < SDHCI_SPEC_300)
+	if (host->version < SDHCI_SPEC_300 ||
+	    (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
+	     host->version >= SDHCI_SPEC_400 &&
+	     host->mmc->flags & MMC_UHS2_SUPPORT))
 		return 0;
 
 	ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
-- 
2.27.0

Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[Adrian Hunter]

On 10/07/20 2:11 pm, Ben Chuang wrote:
> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> 
> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
> and not for UHS-II mode.
> 
> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> ---
>  drivers/mmc/host/sdhci.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 5511649946b9..7f2537648a08 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
>  	/*
>  	 * Signal Voltage Switching is only applicable for Host Controllers
>  	 * v3.00 and above.
> +	 * But for UHS2, the signal voltage is supplied by vdd2 which is
> +	 * already 1.8v so no voltage switch required.
>  	 */
> -	if (host->version < SDHCI_SPEC_300)
> +	if (host->version < SDHCI_SPEC_300 ||
> +	    (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> +	     host->version >= SDHCI_SPEC_400 &&
> +	     host->mmc->flags & MMC_UHS2_SUPPORT))

Please look at hooking ->start_signal_voltage_switch() instead


>  		return 0;
>  
>  	ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
> 

Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[AKASHI Takahiro]

Adrian,

On Fri, Aug 21, 2020 at 05:09:01PM +0300, Adrian Hunter wrote:
> On 10/07/20 2:11 pm, Ben Chuang wrote:
> > From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > 
> > sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
> > and not for UHS-II mode.
> > 
> > Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > ---
> >  drivers/mmc/host/sdhci.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > index 5511649946b9..7f2537648a08 100644
> > --- a/drivers/mmc/host/sdhci.c
> > +++ b/drivers/mmc/host/sdhci.c
> > @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
> >  	/*
> >  	 * Signal Voltage Switching is only applicable for Host Controllers
> >  	 * v3.00 and above.
> > +	 * But for UHS2, the signal voltage is supplied by vdd2 which is
> > +	 * already 1.8v so no voltage switch required.
> >  	 */
> > -	if (host->version < SDHCI_SPEC_300)
> > +	if (host->version < SDHCI_SPEC_300 ||
> > +	    (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> > +	     host->version >= SDHCI_SPEC_400 &&
> > +	     host->mmc->flags & MMC_UHS2_SUPPORT))
> 
> Please look at hooking ->start_signal_voltage_switch() instead

Do you mean that you want every platform driver who wants to support UHS-II
to set NULL to start_signal_voltage_switch hook even if this hack is
platform agnostic?
(Another option is that it would be put in sdhci_uhs2_add_host() which
is responsible to set MMC_UHS2_SUPPORT.)

-Takahiro Akashi

> 
> 
> >  		return 0;
> >  
> >  	ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
> > 
> 

Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[Adrian Hunter]

On 14/09/20 9:40 am, AKASHI Takahiro wrote:
> Adrian,
> 
> On Fri, Aug 21, 2020 at 05:09:01PM +0300, Adrian Hunter wrote:
>> On 10/07/20 2:11 pm, Ben Chuang wrote:
>>> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
>>>
>>> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
>>> and not for UHS-II mode.
>>>
>>> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>>> ---
>>>  drivers/mmc/host/sdhci.c | 7 ++++++-
>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>>> index 5511649946b9..7f2537648a08 100644
>>> --- a/drivers/mmc/host/sdhci.c
>>> +++ b/drivers/mmc/host/sdhci.c
>>> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
>>>  	/*
>>>  	 * Signal Voltage Switching is only applicable for Host Controllers
>>>  	 * v3.00 and above.
>>> +	 * But for UHS2, the signal voltage is supplied by vdd2 which is
>>> +	 * already 1.8v so no voltage switch required.
>>>  	 */
>>> -	if (host->version < SDHCI_SPEC_300)
>>> +	if (host->version < SDHCI_SPEC_300 ||
>>> +	    (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
>>> +	     host->version >= SDHCI_SPEC_400 &&
>>> +	     host->mmc->flags & MMC_UHS2_SUPPORT))
>>
>> Please look at hooking ->start_signal_voltage_switch() instead
> 
> Do you mean that you want every platform driver who wants to support UHS-II
> to set NULL to start_signal_voltage_switch hook even if this hack is
> platform agnostic?

No, I see UHS-II as a separate layer i.e.

 UHS-II host controller driver
  |   |
  |   v
  |   sdhci-uhs2 e.g. sdhci_uhs2_start_signal_voltage_switch
  |   |
  v   v
  sdhci e.g. sdhci_start_signal_voltage_switch

Most things should go through sdhci-uhs2 but not nessarily everything.

Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[AKASHI Takahiro]

Ben, Adrian,

On Mon, Sep 14, 2020 at 11:08:14AM +0300, Adrian Hunter wrote:
> On 14/09/20 9:40 am, AKASHI Takahiro wrote:
> > Adrian,
> > 
> > On Fri, Aug 21, 2020 at 05:09:01PM +0300, Adrian Hunter wrote:
> >> On 10/07/20 2:11 pm, Ben Chuang wrote:
> >>> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> >>>
> >>> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
> >>> and not for UHS-II mode.
> >>>
> >>> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> >>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> >>> ---
> >>>  drivers/mmc/host/sdhci.c | 7 ++++++-
> >>>  1 file changed, 6 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> >>> index 5511649946b9..7f2537648a08 100644
> >>> --- a/drivers/mmc/host/sdhci.c
> >>> +++ b/drivers/mmc/host/sdhci.c
> >>> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
> >>>  	/*
> >>>  	 * Signal Voltage Switching is only applicable for Host Controllers
> >>>  	 * v3.00 and above.
> >>> +	 * But for UHS2, the signal voltage is supplied by vdd2 which is
> >>> +	 * already 1.8v so no voltage switch required.

I have been confused with this comment.
(I know it came from the original Intel code, not from Ben.)

If this comment is true,

> >>>  	 */
> >>> -	if (host->version < SDHCI_SPEC_300)
> >>> +	if (host->version < SDHCI_SPEC_300 ||
> >>> +	    (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> >>> +	     host->version >= SDHCI_SPEC_400 &&
> >>> +	     host->mmc->flags & MMC_UHS2_SUPPORT))

the condition above must be wrong since 'flags & MMC_UHS2_SUPPORT'
is one of capabilities for a host controller, not a card
while the selection of voltage depends on a card type.

So I wonder why this code still works.
I guess that it is because set_signal_voltage(), or other variant functions,
will never be called for UHS-II cards under the current implementation.

Looking at mmc_sd_init_card(), we have added some hack:
mmc_sd_init_card()
{
        ...
        /* For UHS2, skip the UHS-I initialization. */
        if ((host->flags & MMC_UHS2_SUPPORT) &&
            (host->flags & MMC_UHS2_INITIALIZED))
                goto done;
        ...
                if (mmc_sd_card_using_v18(card)) {
                        if (mmc_host_set_uhs_voltage(host) ||
                            mmc_sd_init_uhs_card(card)) {
                ...
}

Ben, can you confirm this?
(There is another callsite of mmc_host_set_uhs_voltage() though.)

> >> Please look at hooking ->start_signal_voltage_switch() instead
> > 
> > Do you mean that you want every platform driver who wants to support UHS-II
> > to set NULL to start_signal_voltage_switch hook even if this hack is
> > platform agnostic?
> 
> No, I see UHS-II as a separate layer i.e.
> 
>  UHS-II host controller driver
>   |   |
>   |   v
>   |   sdhci-uhs2 e.g. sdhci_uhs2_start_signal_voltage_switch
>   |   |
>   v   v
>   sdhci e.g. sdhci_start_signal_voltage_switch
> 
> Most things should go through sdhci-uhs2 but not nessarily everything.

What I meant by my previous comment is that we don't have to
call any function, sdhci_uhs2_start_signal_voltage_switch in above example,
for UHS-II cards in any case since it is always simply empty.

-Takahiro Akashi

Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[Ben Chuang]

Hi Takahiro,

On Tue, Sep 15, 2020 at 2:03 PM AKASHI Takahiro
<takahiro.akashi@linaro.org> wrote:
>
> Ben, Adrian,
>
> On Mon, Sep 14, 2020 at 11:08:14AM +0300, Adrian Hunter wrote:
> > On 14/09/20 9:40 am, AKASHI Takahiro wrote:
> > > Adrian,
> > >
> > > On Fri, Aug 21, 2020 at 05:09:01PM +0300, Adrian Hunter wrote:
> > >> On 10/07/20 2:11 pm, Ben Chuang wrote:
> > >>> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > >>>
> > >>> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
> > >>> and not for UHS-II mode.
> > >>>
> > >>> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> > >>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > >>> ---
> > >>>  drivers/mmc/host/sdhci.c | 7 ++++++-
> > >>>  1 file changed, 6 insertions(+), 1 deletion(-)
> > >>>
> > >>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > >>> index 5511649946b9..7f2537648a08 100644
> > >>> --- a/drivers/mmc/host/sdhci.c
> > >>> +++ b/drivers/mmc/host/sdhci.c
> > >>> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
> > >>>   /*
> > >>>    * Signal Voltage Switching is only applicable for Host Controllers
> > >>>    * v3.00 and above.
> > >>> +  * But for UHS2, the signal voltage is supplied by vdd2 which is
> > >>> +  * already 1.8v so no voltage switch required.
>
> I have been confused with this comment.
> (I know it came from the original Intel code, not from Ben.)
>
> If this comment is true,
>
> > >>>    */
> > >>> - if (host->version < SDHCI_SPEC_300)
> > >>> + if (host->version < SDHCI_SPEC_300 ||
> > >>> +     (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> > >>> +      host->version >= SDHCI_SPEC_400 &&
> > >>> +      host->mmc->flags & MMC_UHS2_SUPPORT))
>
> the condition above must be wrong since 'flags & MMC_UHS2_SUPPORT'
> is one of capabilities for a host controller, not a card
> while the selection of voltage depends on a card type.

The flag MMC_UHS2_SUPPORT is set at the beginning of mmc_uhs2_rescan_try_freq().
In UHS-II flow, it stays set.
If the attempt to UHS-II fails finally, it will be unset.

>
> So I wonder why this code still works.
> I guess that it is because set_signal_voltage(), or other variant functions,
> will never be called for UHS-II cards under the current implementation.
>
> Looking at mmc_sd_init_card(), we have added some hack:
> mmc_sd_init_card()
> {
>         ...
>         /* For UHS2, skip the UHS-I initialization. */
>         if ((host->flags & MMC_UHS2_SUPPORT) &&
>             (host->flags & MMC_UHS2_INITIALIZED))
>                 goto done;
>         ...
>                 if (mmc_sd_card_using_v18(card)) {
>                         if (mmc_host_set_uhs_voltage(host) ||
>                             mmc_sd_init_uhs_card(card)) {
>                 ...
> }
>
> Ben, can you confirm this?
> (There is another callsite of mmc_host_set_uhs_voltage() though.)

UHS-II cards use differential signals and don't need to signal voltage switch.
But the main task is to set the parameters of UHS-II card interface.

>
> > >> Please look at hooking ->start_signal_voltage_switch() instead
> > >
> > > Do you mean that you want every platform driver who wants to support UHS-II
> > > to set NULL to start_signal_voltage_switch hook even if this hack is
> > > platform agnostic?
> >
> > No, I see UHS-II as a separate layer i.e.
> >
> >  UHS-II host controller driver
> >   |   |
> >   |   v
> >   |   sdhci-uhs2 e.g. sdhci_uhs2_start_signal_voltage_switch
> >   |   |
> >   v   v
> >   sdhci e.g. sdhci_start_signal_voltage_switch
> >
> > Most things should go through sdhci-uhs2 but not nessarily everything.
>
> What I meant by my previous comment is that we don't have to
> call any function, sdhci_uhs2_start_signal_voltage_switch in above example,
> for UHS-II cards in any case since it is always simply empty.
>
> -Takahiro Akashi

Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[AKASHI Takahiro]

On Tue, Sep 15, 2020 at 07:36:14PM +0800, Ben Chuang wrote:
> Hi Takahiro,
> 
> On Tue, Sep 15, 2020 at 2:03 PM AKASHI Takahiro
> <takahiro.akashi@linaro.org> wrote:
> >
> > Ben, Adrian,
> >
> > On Mon, Sep 14, 2020 at 11:08:14AM +0300, Adrian Hunter wrote:
> > > On 14/09/20 9:40 am, AKASHI Takahiro wrote:
> > > > Adrian,
> > > >
> > > > On Fri, Aug 21, 2020 at 05:09:01PM +0300, Adrian Hunter wrote:
> > > >> On 10/07/20 2:11 pm, Ben Chuang wrote:
> > > >>> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > > >>>
> > > >>> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
> > > >>> and not for UHS-II mode.
> > > >>>
> > > >>> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> > > >>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > > >>> ---
> > > >>>  drivers/mmc/host/sdhci.c | 7 ++++++-
> > > >>>  1 file changed, 6 insertions(+), 1 deletion(-)
> > > >>>
> > > >>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > > >>> index 5511649946b9..7f2537648a08 100644
> > > >>> --- a/drivers/mmc/host/sdhci.c
> > > >>> +++ b/drivers/mmc/host/sdhci.c
> > > >>> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
> > > >>>   /*
> > > >>>    * Signal Voltage Switching is only applicable for Host Controllers
> > > >>>    * v3.00 and above.
> > > >>> +  * But for UHS2, the signal voltage is supplied by vdd2 which is
> > > >>> +  * already 1.8v so no voltage switch required.
> >
> > I have been confused with this comment.
> > (I know it came from the original Intel code, not from Ben.)
> >
> > If this comment is true,
> >
> > > >>>    */
> > > >>> - if (host->version < SDHCI_SPEC_300)
> > > >>> + if (host->version < SDHCI_SPEC_300 ||
> > > >>> +     (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> > > >>> +      host->version >= SDHCI_SPEC_400 &&
> > > >>> +      host->mmc->flags & MMC_UHS2_SUPPORT))
> >
> > the condition above must be wrong since 'flags & MMC_UHS2_SUPPORT'
> > is one of capabilities for a host controller, not a card
> > while the selection of voltage depends on a card type.
> 
> The flag MMC_UHS2_SUPPORT is set at the beginning of mmc_uhs2_rescan_try_freq().
> In UHS-II flow, it stays set.
> If the attempt to UHS-II fails finally, it will be unset.

Right, but MMC_UHS2_SUPPORT is also set, at least initially,
in sdhci_uhs2_add_host(). It is confusing, isn't it?

As we discussed before, any card-specific properties, like UHS-II mode,
should be placed in a card structure, not a host structure.

> >
> > So I wonder why this code still works.
> > I guess that it is because set_signal_voltage(), or other variant functions,
> > will never be called for UHS-II cards under the current implementation.
> >
> > Looking at mmc_sd_init_card(), we have added some hack:
> > mmc_sd_init_card()
> > {
> >         ...
> >         /* For UHS2, skip the UHS-I initialization. */
> >         if ((host->flags & MMC_UHS2_SUPPORT) &&
> >             (host->flags & MMC_UHS2_INITIALIZED))
> >                 goto done;
> >         ...
> >                 if (mmc_sd_card_using_v18(card)) {
> >                         if (mmc_host_set_uhs_voltage(host) ||
> >                             mmc_sd_init_uhs_card(card)) {
> >                 ...
> > }
> >
> > Ben, can you confirm this?
> > (There is another callsite of mmc_host_set_uhs_voltage() though.)
> 
> UHS-II cards use differential signals and don't need to signal voltage switch.
> But the main task is to set the parameters of UHS-II card interface.

Whoever sets MMC_UHS2_SUPPORT (and MMC_UHS2_INITIALIZED), my assertion above
(mmc_host_set_uhs_voltage, and hence [sdhci_]start_signal_voltage_switch(), is
never called for UHS-II cards) will be valid, isn't it?

-Takahiro Akashi

> >
> > > >> Please look at hooking ->start_signal_voltage_switch() instead
> > > >
> > > > Do you mean that you want every platform driver who wants to support UHS-II
> > > > to set NULL to start_signal_voltage_switch hook even if this hack is
> > > > platform agnostic?
> > >
> > > No, I see UHS-II as a separate layer i.e.
> > >
> > >  UHS-II host controller driver
> > >   |   |
> > >   |   v
> > >   |   sdhci-uhs2 e.g. sdhci_uhs2_start_signal_voltage_switch
> > >   |   |
> > >   v   v
> > >   sdhci e.g. sdhci_start_signal_voltage_switch
> > >
> > > Most things should go through sdhci-uhs2 but not nessarily everything.
> >
> > What I meant by my previous comment is that we don't have to
> > call any function, sdhci_uhs2_start_signal_voltage_switch in above example,
> > for UHS-II cards in any case since it is always simply empty.
> >
> > -Takahiro Akashi

Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[Ben Chuang]

On Wed, Sep 16, 2020 at 8:52 AM AKASHI Takahiro
<takahiro.akashi@linaro.org> wrote:
>
> On Tue, Sep 15, 2020 at 07:36:14PM +0800, Ben Chuang wrote:
> > Hi Takahiro,
> >
> > On Tue, Sep 15, 2020 at 2:03 PM AKASHI Takahiro
> > <takahiro.akashi@linaro.org> wrote:
> > >
> > > Ben, Adrian,
> > >
> > > On Mon, Sep 14, 2020 at 11:08:14AM +0300, Adrian Hunter wrote:
> > > > On 14/09/20 9:40 am, AKASHI Takahiro wrote:
> > > > > Adrian,
> > > > >
> > > > > On Fri, Aug 21, 2020 at 05:09:01PM +0300, Adrian Hunter wrote:
> > > > >> On 10/07/20 2:11 pm, Ben Chuang wrote:
> > > > >>> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > > > >>>
> > > > >>> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
> > > > >>> and not for UHS-II mode.
> > > > >>>
> > > > >>> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> > > > >>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > > > >>> ---
> > > > >>>  drivers/mmc/host/sdhci.c | 7 ++++++-
> > > > >>>  1 file changed, 6 insertions(+), 1 deletion(-)
> > > > >>>
> > > > >>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > > > >>> index 5511649946b9..7f2537648a08 100644
> > > > >>> --- a/drivers/mmc/host/sdhci.c
> > > > >>> +++ b/drivers/mmc/host/sdhci.c
> > > > >>> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
> > > > >>>   /*
> > > > >>>    * Signal Voltage Switching is only applicable for Host Controllers
> > > > >>>    * v3.00 and above.
> > > > >>> +  * But for UHS2, the signal voltage is supplied by vdd2 which is
> > > > >>> +  * already 1.8v so no voltage switch required.
> > >
> > > I have been confused with this comment.
> > > (I know it came from the original Intel code, not from Ben.)
> > >
> > > If this comment is true,
> > >
> > > > >>>    */
> > > > >>> - if (host->version < SDHCI_SPEC_300)
> > > > >>> + if (host->version < SDHCI_SPEC_300 ||
> > > > >>> +     (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> > > > >>> +      host->version >= SDHCI_SPEC_400 &&
> > > > >>> +      host->mmc->flags & MMC_UHS2_SUPPORT))
> > >
> > > the condition above must be wrong since 'flags & MMC_UHS2_SUPPORT'
> > > is one of capabilities for a host controller, not a card
> > > while the selection of voltage depends on a card type.
> >
> > The flag MMC_UHS2_SUPPORT is set at the beginning of mmc_uhs2_rescan_try_freq().
> > In UHS-II flow, it stays set.
> > If the attempt to UHS-II fails finally, it will be unset.
>
> Right, but MMC_UHS2_SUPPORT is also set, at least initially,
> in sdhci_uhs2_add_host(). It is confusing, isn't it?

I think it can be removed from sdhci_uhs2_add_host() to avoid making confusion.

>
> As we discussed before, any card-specific properties, like UHS-II mode,
> should be placed in a card structure, not a host structure.
>
> > >
> > > So I wonder why this code still works.
> > > I guess that it is because set_signal_voltage(), or other variant functions,
> > > will never be called for UHS-II cards under the current implementation.
> > >
> > > Looking at mmc_sd_init_card(), we have added some hack:
> > > mmc_sd_init_card()
> > > {
> > >         ...
> > >         /* For UHS2, skip the UHS-I initialization. */
> > >         if ((host->flags & MMC_UHS2_SUPPORT) &&
> > >             (host->flags & MMC_UHS2_INITIALIZED))
> > >                 goto done;
> > >         ...
> > >                 if (mmc_sd_card_using_v18(card)) {
> > >                         if (mmc_host_set_uhs_voltage(host) ||
> > >                             mmc_sd_init_uhs_card(card)) {
> > >                 ...
> > > }
> > >
> > > Ben, can you confirm this?
> > > (There is another callsite of mmc_host_set_uhs_voltage() though.)
> >
> > UHS-II cards use differential signals and don't need to signal voltage switch.
> > But the main task is to set the parameters of UHS-II card interface.
>
> Whoever sets MMC_UHS2_SUPPORT (and MMC_UHS2_INITIALIZED), my assertion above
> (mmc_host_set_uhs_voltage, and hence [sdhci_]start_signal_voltage_switch(), is
> never called for UHS-II cards) will be valid, isn't it?
>
> -Takahiro Akashi
>
> > >
> > > > >> Please look at hooking ->start_signal_voltage_switch() instead
> > > > >
> > > > > Do you mean that you want every platform driver who wants to support UHS-II
> > > > > to set NULL to start_signal_voltage_switch hook even if this hack is
> > > > > platform agnostic?
> > > >
> > > > No, I see UHS-II as a separate layer i.e.
> > > >
> > > >  UHS-II host controller driver
> > > >   |   |
> > > >   |   v
> > > >   |   sdhci-uhs2 e.g. sdhci_uhs2_start_signal_voltage_switch
> > > >   |   |
> > > >   v   v
> > > >   sdhci e.g. sdhci_start_signal_voltage_switch
> > > >
> > > > Most things should go through sdhci-uhs2 but not nessarily everything.
> > >
> > > What I meant by my previous comment is that we don't have to
> > > call any function, sdhci_uhs2_start_signal_voltage_switch in above example,
> > > for UHS-II cards in any case since it is always simply empty.
> > >
> > > -Takahiro Akashi

Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[AKASHI Takahiro]

Ben,

On Wed, Sep 16, 2020 at 05:42:07PM +0800, Ben Chuang wrote:
> On Wed, Sep 16, 2020 at 8:52 AM AKASHI Takahiro
> <takahiro.akashi@linaro.org> wrote:
> >
> > On Tue, Sep 15, 2020 at 07:36:14PM +0800, Ben Chuang wrote:
> > > Hi Takahiro,
> > >
> > > On Tue, Sep 15, 2020 at 2:03 PM AKASHI Takahiro
> > > <takahiro.akashi@linaro.org> wrote:
> > > >
> > > > Ben, Adrian,
> > > >
> > > > On Mon, Sep 14, 2020 at 11:08:14AM +0300, Adrian Hunter wrote:
> > > > > On 14/09/20 9:40 am, AKASHI Takahiro wrote:
> > > > > > Adrian,
> > > > > >
> > > > > > On Fri, Aug 21, 2020 at 05:09:01PM +0300, Adrian Hunter wrote:
> > > > > >> On 10/07/20 2:11 pm, Ben Chuang wrote:
> > > > > >>> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > > > > >>>
> > > > > >>> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
> > > > > >>> and not for UHS-II mode.
> > > > > >>>
> > > > > >>> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> > > > > >>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > > > > >>> ---
> > > > > >>>  drivers/mmc/host/sdhci.c | 7 ++++++-
> > > > > >>>  1 file changed, 6 insertions(+), 1 deletion(-)
> > > > > >>>
> > > > > >>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > > > > >>> index 5511649946b9..7f2537648a08 100644
> > > > > >>> --- a/drivers/mmc/host/sdhci.c
> > > > > >>> +++ b/drivers/mmc/host/sdhci.c
> > > > > >>> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
> > > > > >>>   /*
> > > > > >>>    * Signal Voltage Switching is only applicable for Host Controllers
> > > > > >>>    * v3.00 and above.
> > > > > >>> +  * But for UHS2, the signal voltage is supplied by vdd2 which is
> > > > > >>> +  * already 1.8v so no voltage switch required.
> > > >
> > > > I have been confused with this comment.
> > > > (I know it came from the original Intel code, not from Ben.)
> > > >
> > > > If this comment is true,
> > > >
> > > > > >>>    */
> > > > > >>> - if (host->version < SDHCI_SPEC_300)
> > > > > >>> + if (host->version < SDHCI_SPEC_300 ||
> > > > > >>> +     (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> > > > > >>> +      host->version >= SDHCI_SPEC_400 &&
> > > > > >>> +      host->mmc->flags & MMC_UHS2_SUPPORT))
> > > >
> > > > the condition above must be wrong since 'flags & MMC_UHS2_SUPPORT'
> > > > is one of capabilities for a host controller, not a card
> > > > while the selection of voltage depends on a card type.
> > >
> > > The flag MMC_UHS2_SUPPORT is set at the beginning of mmc_uhs2_rescan_try_freq().
> > > In UHS-II flow, it stays set.
> > > If the attempt to UHS-II fails finally, it will be unset.
> >
> > Right, but MMC_UHS2_SUPPORT is also set, at least initially,
> > in sdhci_uhs2_add_host(). It is confusing, isn't it?
> 
> I think it can be removed from sdhci_uhs2_add_host() to avoid making confusion.

Okay,

> >
> > As we discussed before, any card-specific properties, like UHS-II mode,
> > should be placed in a card structure, not a host structure.

Do you have any idea on this?
I remember that Ulf also made a similar comment on the "core" side.

-Takahiro Akashi

> >
> > > >
> > > > So I wonder why this code still works.
> > > > I guess that it is because set_signal_voltage(), or other variant functions,
> > > > will never be called for UHS-II cards under the current implementation.
> > > >
> > > > Looking at mmc_sd_init_card(), we have added some hack:
> > > > mmc_sd_init_card()
> > > > {
> > > >         ...
> > > >         /* For UHS2, skip the UHS-I initialization. */
> > > >         if ((host->flags & MMC_UHS2_SUPPORT) &&
> > > >             (host->flags & MMC_UHS2_INITIALIZED))
> > > >                 goto done;
> > > >         ...
> > > >                 if (mmc_sd_card_using_v18(card)) {
> > > >                         if (mmc_host_set_uhs_voltage(host) ||
> > > >                             mmc_sd_init_uhs_card(card)) {
> > > >                 ...
> > > > }
> > > >
> > > > Ben, can you confirm this?
> > > > (There is another callsite of mmc_host_set_uhs_voltage() though.)
> > >
> > > UHS-II cards use differential signals and don't need to signal voltage switch.
> > > But the main task is to set the parameters of UHS-II card interface.
> >
> > Whoever sets MMC_UHS2_SUPPORT (and MMC_UHS2_INITIALIZED), my assertion above
> > (mmc_host_set_uhs_voltage, and hence [sdhci_]start_signal_voltage_switch(), is
> > never called for UHS-II cards) will be valid, isn't it?
> >
> > -Takahiro Akashi
> >
> > > >
> > > > > >> Please look at hooking ->start_signal_voltage_switch() instead
> > > > > >
> > > > > > Do you mean that you want every platform driver who wants to support UHS-II
> > > > > > to set NULL to start_signal_voltage_switch hook even if this hack is
> > > > > > platform agnostic?
> > > > >
> > > > > No, I see UHS-II as a separate layer i.e.
> > > > >
> > > > >  UHS-II host controller driver
> > > > >   |   |
> > > > >   |   v
> > > > >   |   sdhci-uhs2 e.g. sdhci_uhs2_start_signal_voltage_switch
> > > > >   |   |
> > > > >   v   v
> > > > >   sdhci e.g. sdhci_start_signal_voltage_switch
> > > > >
> > > > > Most things should go through sdhci-uhs2 but not nessarily everything.
> > > >
> > > > What I meant by my previous comment is that we don't have to
> > > > call any function, sdhci_uhs2_start_signal_voltage_switch in above example,
> > > > for UHS-II cards in any case since it is always simply empty.
> > > >
> > > > -Takahiro Akashi

Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[Ben Chuang]

On Thu, Sep 17, 2020 at 8:56 AM AKASHI Takahiro
<takahiro.akashi@linaro.org> wrote:
>
> Ben,
>
> On Wed, Sep 16, 2020 at 05:42:07PM +0800, Ben Chuang wrote:
> > On Wed, Sep 16, 2020 at 8:52 AM AKASHI Takahiro
> > <takahiro.akashi@linaro.org> wrote:
> > >
> > > On Tue, Sep 15, 2020 at 07:36:14PM +0800, Ben Chuang wrote:
> > > > Hi Takahiro,
> > > >
> > > > On Tue, Sep 15, 2020 at 2:03 PM AKASHI Takahiro
> > > > <takahiro.akashi@linaro.org> wrote:
> > > > >
> > > > > Ben, Adrian,
> > > > >
> > > > > On Mon, Sep 14, 2020 at 11:08:14AM +0300, Adrian Hunter wrote:
> > > > > > On 14/09/20 9:40 am, AKASHI Takahiro wrote:
> > > > > > > Adrian,
> > > > > > >
> > > > > > > On Fri, Aug 21, 2020 at 05:09:01PM +0300, Adrian Hunter wrote:
> > > > > > >> On 10/07/20 2:11 pm, Ben Chuang wrote:
> > > > > > >>> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > > > > > >>>
> > > > > > >>> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
> > > > > > >>> and not for UHS-II mode.
> > > > > > >>>
> > > > > > >>> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> > > > > > >>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > > > > > >>> ---
> > > > > > >>>  drivers/mmc/host/sdhci.c | 7 ++++++-
> > > > > > >>>  1 file changed, 6 insertions(+), 1 deletion(-)
> > > > > > >>>
> > > > > > >>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > > > > > >>> index 5511649946b9..7f2537648a08 100644
> > > > > > >>> --- a/drivers/mmc/host/sdhci.c
> > > > > > >>> +++ b/drivers/mmc/host/sdhci.c
> > > > > > >>> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
> > > > > > >>>   /*
> > > > > > >>>    * Signal Voltage Switching is only applicable for Host Controllers
> > > > > > >>>    * v3.00 and above.
> > > > > > >>> +  * But for UHS2, the signal voltage is supplied by vdd2 which is
> > > > > > >>> +  * already 1.8v so no voltage switch required.
> > > > >
> > > > > I have been confused with this comment.
> > > > > (I know it came from the original Intel code, not from Ben.)
> > > > >
> > > > > If this comment is true,
> > > > >
> > > > > > >>>    */
> > > > > > >>> - if (host->version < SDHCI_SPEC_300)
> > > > > > >>> + if (host->version < SDHCI_SPEC_300 ||
> > > > > > >>> +     (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> > > > > > >>> +      host->version >= SDHCI_SPEC_400 &&
> > > > > > >>> +      host->mmc->flags & MMC_UHS2_SUPPORT))
> > > > >
> > > > > the condition above must be wrong since 'flags & MMC_UHS2_SUPPORT'
> > > > > is one of capabilities for a host controller, not a card
> > > > > while the selection of voltage depends on a card type.
> > > >
> > > > The flag MMC_UHS2_SUPPORT is set at the beginning of mmc_uhs2_rescan_try_freq().
> > > > In UHS-II flow, it stays set.
> > > > If the attempt to UHS-II fails finally, it will be unset.
> > >
> > > Right, but MMC_UHS2_SUPPORT is also set, at least initially,
> > > in sdhci_uhs2_add_host(). It is confusing, isn't it?
> >
> > I think it can be removed from sdhci_uhs2_add_host() to avoid making confusion.
>
> Okay,
>
> > >
> > > As we discussed before, any card-specific properties, like UHS-II mode,
> > > should be placed in a card structure, not a host structure.
>
> Do you have any idea on this?
> I remember that Ulf also made a similar comment on the "core" side.

We may list those properties to do first. i.e. MMC_UHS2_INITIALIZED.

>
> -Takahiro Akashi
>
> > >
> > > > >
> > > > > So I wonder why this code still works.
> > > > > I guess that it is because set_signal_voltage(), or other variant functions,
> > > > > will never be called for UHS-II cards under the current implementation.
> > > > >
> > > > > Looking at mmc_sd_init_card(), we have added some hack:
> > > > > mmc_sd_init_card()
> > > > > {
> > > > >         ...
> > > > >         /* For UHS2, skip the UHS-I initialization. */
> > > > >         if ((host->flags & MMC_UHS2_SUPPORT) &&
> > > > >             (host->flags & MMC_UHS2_INITIALIZED))
> > > > >                 goto done;
> > > > >         ...
> > > > >                 if (mmc_sd_card_using_v18(card)) {
> > > > >                         if (mmc_host_set_uhs_voltage(host) ||
> > > > >                             mmc_sd_init_uhs_card(card)) {
> > > > >                 ...
> > > > > }
> > > > >
> > > > > Ben, can you confirm this?
> > > > > (There is another callsite of mmc_host_set_uhs_voltage() though.)
> > > >
> > > > UHS-II cards use differential signals and don't need to signal voltage switch.
> > > > But the main task is to set the parameters of UHS-II card interface.
> > >
> > > Whoever sets MMC_UHS2_SUPPORT (and MMC_UHS2_INITIALIZED), my assertion above
> > > (mmc_host_set_uhs_voltage, and hence [sdhci_]start_signal_voltage_switch(), is
> > > never called for UHS-II cards) will be valid, isn't it?
> > >
> > > -Takahiro Akashi
> > >
> > > > >
> > > > > > >> Please look at hooking ->start_signal_voltage_switch() instead
> > > > > > >
> > > > > > > Do you mean that you want every platform driver who wants to support UHS-II
> > > > > > > to set NULL to start_signal_voltage_switch hook even if this hack is
> > > > > > > platform agnostic?
> > > > > >
> > > > > > No, I see UHS-II as a separate layer i.e.
> > > > > >
> > > > > >  UHS-II host controller driver
> > > > > >   |   |
> > > > > >   |   v
> > > > > >   |   sdhci-uhs2 e.g. sdhci_uhs2_start_signal_voltage_switch
> > > > > >   |   |
> > > > > >   v   v
> > > > > >   sdhci e.g. sdhci_start_signal_voltage_switch
> > > > > >
> > > > > > Most things should go through sdhci-uhs2 but not nessarily everything.
> > > > >
> > > > > What I meant by my previous comment is that we don't have to
> > > > > call any function, sdhci_uhs2_start_signal_voltage_switch in above example,
> > > > > for UHS-II cards in any case since it is always simply empty.
> > > > >
> > > > > -Takahiro Akashi

Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip signal_voltage_switch()

[AKASHI Takahiro]

On Wed, Sep 16, 2020 at 09:01:20AM +0300, Adrian Hunter wrote:
> On 15/09/20 9:03 am, AKASHI Takahiro wrote:
> > Ben, Adrian,
> > 
> > On Mon, Sep 14, 2020 at 11:08:14AM +0300, Adrian Hunter wrote:
> >> On 14/09/20 9:40 am, AKASHI Takahiro wrote:
> >>> Adrian,
> >>>
> >>> On Fri, Aug 21, 2020 at 05:09:01PM +0300, Adrian Hunter wrote:
> >>>> On 10/07/20 2:11 pm, Ben Chuang wrote:
> >>>>> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> >>>>>
> >>>>> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
> >>>>> and not for UHS-II mode.
> >>>>>
> >>>>> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> >>>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> >>>>> ---
> >>>>>  drivers/mmc/host/sdhci.c | 7 ++++++-
> >>>>>  1 file changed, 6 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> >>>>> index 5511649946b9..7f2537648a08 100644
> >>>>> --- a/drivers/mmc/host/sdhci.c
> >>>>> +++ b/drivers/mmc/host/sdhci.c
> >>>>> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
> >>>>>  	/*
> >>>>>  	 * Signal Voltage Switching is only applicable for Host Controllers
> >>>>>  	 * v3.00 and above.
> >>>>> +	 * But for UHS2, the signal voltage is supplied by vdd2 which is
> >>>>> +	 * already 1.8v so no voltage switch required.
> >>>>>  	 */
> >>>>> -	if (host->version < SDHCI_SPEC_300)
> >>>>> +	if (host->version < SDHCI_SPEC_300 ||
> >>>>> +	    (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> >>>>> +	     host->version >= SDHCI_SPEC_400 &&
> >>>>> +	     host->mmc->flags & MMC_UHS2_SUPPORT))
> >>>> Please look at hooking ->start_signal_voltage_switch() instead
> >>>
> >>> Do you mean that you want every platform driver who wants to support UHS-II
> >>> to set NULL to start_signal_voltage_switch hook even if this hack is
> >>> platform agnostic?
> >>
> >> No, I see UHS-II as a separate layer i.e.
> >>
> >>  UHS-II host controller driver
> >>   |   |
> >>   |   v
> >>   |   sdhci-uhs2 e.g. sdhci_uhs2_start_signal_voltage_switch
> >>   |   |
> >>   v   v
> >>   sdhci e.g. sdhci_start_signal_voltage_switch
> >>
> >> Most things should go through sdhci-uhs2 but not nessarily everything.
> > 
> > What I meant by my previous comment is that we don't have to
> > call any function, sdhci_uhs2_start_signal_voltage_switch in above example,
> > for UHS-II cards in any case since it is always simply empty.
> 
> Please treat the sdhci_uhs2_... host ops as functions for a UHS-II host
> controller in either UHS-II or legacy mode. i.e. it is up to sdhci-uhs2.c to
> call through to sdhci.c not the other way around.  e.g.
>
> int sdhci_uhs2_start_signal_voltage_switch(blah)
> {
> 	if (sdhci_uhs2_mode(host))
> 		return 0;
> 	return sdhci_start_signal_valtage_switch(blah);
> }

Okay, the remaining issue is to clarify the meaning of MMC_UHS2_SUPPORT.

-Takhiro Akashi