[PATCH v2] spi: rockchip: Disable Runtime PM when chip select is asserted

[PATCH v2] spi: rockchip: Disable Runtime PM when chip select is asserted

[Jeffy Chen]

The rockchip spi would stop driving pins when runtime suspended, which
might break slave's xfer(for example cros_ec).

Since we have pullups on those pins, we only need to care about the CS
asserted case.

So let's keep the spi alive when chip select is asserted for that.

Also change use pm_runtime_put instead of pm_runtime_put_sync.

Suggested-by: Doug Anderson <dianders-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
Signed-off-by: Jeffy Chen <jeffy.chen-TNX95d0MmH7DzftRWevZcw@public.gmane.org>

---

Changes in v2:
Improve commit message and comments and coding style.

 drivers/spi/spi-rockchip.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
index acf31f3..ea0edd7 100644
--- a/drivers/spi/spi-rockchip.c
+++ b/drivers/spi/spi-rockchip.c
@@ -264,7 +264,7 @@ static inline u32 rx_max(struct rockchip_spi *rs)
 
 static void rockchip_spi_set_cs(struct spi_device *spi, bool enable)
 {
-	u32 ser;
+	u32 ser, new_ser;
 	struct spi_master *master = spi->master;
 	struct rockchip_spi *rs = spi_master_get_devdata(master);
 
@@ -288,13 +288,26 @@ static void rockchip_spi_set_cs(struct spi_device *spi, bool enable)
 	 * Note: enable(rockchip_spi_set_cs) = !enable(spi_set_cs)
 	 */
 	if (!enable)
-		ser |= 1 << spi->chip_select;
+		new_ser = ser | BIT(spi->chip_select);
 	else
-		ser &= ~(1 << spi->chip_select);
+		new_ser = ser & ~BIT(spi->chip_select);
 
-	writel_relaxed(ser, rs->regs + ROCKCHIP_SPI_SER);
+	if (new_ser != ser) {
+		writel_relaxed(new_ser, rs->regs + ROCKCHIP_SPI_SER);
 
-	pm_runtime_put_sync(rs->dev);
+		/*
+		 * The rockchip spi would stop driving all pins when powered
+		 * down.
+		 * So hold a runtime PM reference as long as CS is asserted.
+		 */
+		if (!enable)
+			return;
+
+		/* Drop reference from when we first asserted CS */
+		pm_runtime_put(rs->dev);
+	}
+
+	pm_runtime_put(rs->dev);
 }
 
 static int rockchip_spi_prepare_message(struct spi_master *master,
-- 
2.1.4


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Re: [PATCH v2] spi: rockchip: Disable Runtime PM when chip select is asserted

[Doug Anderson]

Hi,

On Mon, Jun 26, 2017 at 7:20 PM, Jeffy Chen <jeffy.chen-TNX95d0MmH7DzftRWevZcw@public.gmane.org> wrote:
> The rockchip spi would stop driving pins when runtime suspended, which
> might break slave's xfer(for example cros_ec).
>
> Since we have pullups on those pins, we only need to care about the CS
> asserted case.
>
> So let's keep the spi alive when chip select is asserted for that.
>
> Also change use pm_runtime_put instead of pm_runtime_put_sync.
>
> Suggested-by: Doug Anderson <dianders-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
> Signed-off-by: Jeffy Chen <jeffy.chen-TNX95d0MmH7DzftRWevZcw@public.gmane.org>
>
> ---
>
> Changes in v2:
> Improve commit message and comments and coding style.
>
>  drivers/spi/spi-rockchip.c | 23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
> index acf31f3..ea0edd7 100644
> --- a/drivers/spi/spi-rockchip.c
> +++ b/drivers/spi/spi-rockchip.c
> @@ -264,7 +264,7 @@ static inline u32 rx_max(struct rockchip_spi *rs)
>
>  static void rockchip_spi_set_cs(struct spi_device *spi, bool enable)
>  {
> -       u32 ser;
> +       u32 ser, new_ser;
>         struct spi_master *master = spi->master;
>         struct rockchip_spi *rs = spi_master_get_devdata(master);
>
> @@ -288,13 +288,26 @@ static void rockchip_spi_set_cs(struct spi_device *spi, bool enable)
>          * Note: enable(rockchip_spi_set_cs) = !enable(spi_set_cs)
>          */
>         if (!enable)
> -               ser |= 1 << spi->chip_select;
> +               new_ser = ser | BIT(spi->chip_select);
>         else
> -               ser &= ~(1 << spi->chip_select);
> +               new_ser = ser & ~BIT(spi->chip_select);
>
> -       writel_relaxed(ser, rs->regs + ROCKCHIP_SPI_SER);
> +       if (new_ser != ser) {

IMHO it's not a great idea to use the state of the hardware register
here.  Using the state of the hardware register probably works OK, but
it makes me just a little nervous.  If something happened to the state
of the register (someone used /dev/mem to tweak, or the peripherals
got reset, or ...) then you could end up with an unbalanced set of PM
Runtime calls.  I know none of those things are common, but it still
seems less than great to me.

I'd rather we kept track in "struct rockchip_spi" whether we already
called pm_runtime_get_sync().  AKA the following (untested):

bool cs_asserted = !enable;

/* Return immediately for no-op */
if (cs_asserted == rs->cs_asserted)
  return;

/* Keep things powered as long as CS is asserted */
if (cs_asserted) {
  pm_runtime_get_sync(rs->dev);
  rs->cs_asserted = true;
}

ser = ...
...
...

if (!cs_asserted)
  pm_runtime_put(rs->dev);


NOTE: another advantage of storing the state in 'struct rockchip_spi'
is that you can access it without pm_runtime_get_sync().


> +               writel_relaxed(new_ser, rs->regs + ROCKCHIP_SPI_SER);
>
> -       pm_runtime_put_sync(rs->dev);
> +               /*
> +                * The rockchip spi would stop driving all pins when powered
> +                * down.
> +                * So hold a runtime PM reference as long as CS is asserted.
> +                */
> +               if (!enable)
> +                       return;
> +
> +               /* Drop reference from when we first asserted CS */
> +               pm_runtime_put(rs->dev);
> +       }
> +
> +       pm_runtime_put(rs->dev);

One note is that you should still submit your patch to add
"SPI_MASTER_GPIO_SS" to spi-rockchip.c.  It's important that the SPI
driver see the CS transitions so that it can do the PM Runtime get/put
even when someone uses a GPIO chip select.  Even though the GPIO chip
select will keep state, we don't want the rest of the lines to stop
being driven.


-Doug
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Re: [PATCH v2] spi: rockchip: Disable Runtime PM when chip select is asserted

[jeffy]

Hi doug,

thanx for your comments.

On 06/28/2017 03:27 AM, Doug Anderson wrote:
> Hi,
>
> On Mon, Jun 26, 2017 at 7:20 PM, Jeffy Chen <jeffy.chen-TNX95d0MmH7DzftRWevZcw@public.gmane.org> wrote:
>> The rockchip spi would stop driving pins when runtime suspended, which
>> might break slave's xfer(for example cros_ec).
>>
>> Since we have pullups on those pins, we only need to care about the CS
>> asserted case.
>>
>> So let's keep the spi alive when chip select is asserted for that.
>>
>> Also change use pm_runtime_put instead of pm_runtime_put_sync.
>>
>> Suggested-by: Doug Anderson <dianders-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
>> Signed-off-by: Jeffy Chen <jeffy.chen-TNX95d0MmH7DzftRWevZcw@public.gmane.org>
>>
>> ---
>>
>> Changes in v2:
>> Improve commit message and comments and coding style.
>>
>>   drivers/spi/spi-rockchip.c | 23 ++++++++++++++++++-----
>>   1 file changed, 18 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
>> index acf31f3..ea0edd7 100644
>> --- a/drivers/spi/spi-rockchip.c
>> +++ b/drivers/spi/spi-rockchip.c
>> @@ -264,7 +264,7 @@ static inline u32 rx_max(struct rockchip_spi *rs)
>>
>>   static void rockchip_spi_set_cs(struct spi_device *spi, bool enable)
>>   {
>> -       u32 ser;
>> +       u32 ser, new_ser;
>>          struct spi_master *master = spi->master;
>>          struct rockchip_spi *rs = spi_master_get_devdata(master);
>>
>> @@ -288,13 +288,26 @@ static void rockchip_spi_set_cs(struct spi_device *spi, bool enable)
>>           * Note: enable(rockchip_spi_set_cs) = !enable(spi_set_cs)
>>           */
>>          if (!enable)
>> -               ser |= 1 << spi->chip_select;
>> +               new_ser = ser | BIT(spi->chip_select);
>>          else
>> -               ser &= ~(1 << spi->chip_select);
>> +               new_ser = ser & ~BIT(spi->chip_select);
>>
>> -       writel_relaxed(ser, rs->regs + ROCKCHIP_SPI_SER);
>> +       if (new_ser != ser) {
>
> IMHO it's not a great idea to use the state of the hardware register
> here.  Using the state of the hardware register probably works OK, but
> it makes me just a little nervous.  If something happened to the state
> of the register (someone used /dev/mem to tweak, or the peripherals
> got reset, or ...) then you could end up with an unbalanced set of PM
> Runtime calls.  I know none of those things are common, but it still
> seems less than great to me.
>
> I'd rather we kept track in "struct rockchip_spi" whether we already
> called pm_runtime_get_sync().  AKA the following (untested):
>
> bool cs_asserted = !enable;
>
> /* Return immediately for no-op */
> if (cs_asserted == rs->cs_asserted)
>    return;
>
> /* Keep things powered as long as CS is asserted */
> if (cs_asserted) {
>    pm_runtime_get_sync(rs->dev);
>    rs->cs_asserted = true;
> }
>
> ser = ...
> ...
> ...
>
> if (!cs_asserted)
>    pm_runtime_put(rs->dev);
>
>
> NOTE: another advantage of storing the state in 'struct rockchip_spi'
> is that you can access it without pm_runtime_get_sync().
>
ok, that make sense :)
>
>> +               writel_relaxed(new_ser, rs->regs + ROCKCHIP_SPI_SER);
>>
>> -       pm_runtime_put_sync(rs->dev);
>> +               /*
>> +                * The rockchip spi would stop driving all pins when powered
>> +                * down.
>> +                * So hold a runtime PM reference as long as CS is asserted.
>> +                */
>> +               if (!enable)
>> +                       return;
>> +
>> +               /* Drop reference from when we first asserted CS */
>> +               pm_runtime_put(rs->dev);
>> +       }
>> +
>> +       pm_runtime_put(rs->dev);
>
> One note is that you should still submit your patch to add
> "SPI_MASTER_GPIO_SS" to spi-rockchip.c.  It's important that the SPI
> driver see the CS transitions so that it can do the PM Runtime get/put
> even when someone uses a GPIO chip select.  Even though the GPIO chip
> select will keep state, we don't want the rest of the lines to stop
> being driven.
ok, will do.
>
>
> -Doug
>
>
>


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