Re: [PATCH 2/3] spi: s3c64xx: fix runtime PM handling

[Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>]

On 20.08.2015 04:36, Heiner Kallweit wrote:
> Am 19.08.2015 um 07:54 schrieb Heiner Kallweit:
>> Am 19.08.2015 um 02:35 schrieb Krzysztof Kozlowski:
>>> On 19.08.2015 06:06, Heiner Kallweit wrote:
>>>> The patch fixes / extends the runtime PM handling.
>>>> - Currently the driver instructs the SPI core to use auto-suspend
>>>>   but doesn't configure it. Add the necessary calls and let it
>>>>   autosuspend after probe.
>>>
>>> After quick look at the driver I think it does not use autosuspend
>>> fully. It just sets master->auto_runtime_pm (so the core code will use
>>> autosuspend) but its own calls to pm_runtime_put() are regular ones.
>>> Shouldn't this be enhanced as well?
>> Right, the pm_runtime_put calls in s3c64xx_spi_setup should be
>> replaced as well. Will provide an updated patch.
>>>
>>>> - In case the driver registration fails runtime PM needs to be
>>>>   properly disabled.
>>>>
>>>> Signed-off-by: Heiner Kallweit <hkallweit1@xxxxxxxxx>
>>>> ---
>>>>  drivers/spi/spi-s3c64xx.c | 11 ++++++++++-
>>>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
>>>> index c4d3b06..15a6de1 100644
>>>> --- a/drivers/spi/spi-s3c64xx.c
>>>> +++ b/drivers/spi/spi-s3c64xx.c
>>>> @@ -32,6 +32,7 @@
>>>>  #define MAX_SPI_PORTS		6
>>>>  #define S3C64XX_SPI_QUIRK_POLL		(1 << 0)
>>>>  #define S3C64XX_SPI_QUIRK_CS_AUTO	(1 << 1)
>>>> +#define AUTOSUSPEND_TIMEOUT     2000
>>>>  
>>>>  /* Registers and bit-fields */
>>>>  
>>>> @@ -1180,13 +1181,15 @@ static int s3c64xx_spi_probe(struct platform_device *pdev)
>>>>  	       S3C64XX_SPI_INT_TX_OVERRUN_EN | S3C64XX_SPI_INT_TX_UNDERRUN_EN,
>>>>  	       sdd->regs + S3C64XX_SPI_INT_EN);
>>>>  
>>>> +	pm_runtime_set_autosuspend_delay(dev, AUTOSUSPEND_TIMEOUT);
>>>> +	pm_runtime_use_autosuspend(dev);
>>>>  	pm_runtime_set_active(dev);
>>>>  	pm_runtime_enable(dev);
>>>>  
>>>>  	ret = devm_spi_register_master(dev, master);
>>>>  	if (ret != 0) {
>>>>  		dev_err(dev, "cannot register SPI master: %d\n", ret);
>>>> -		goto err3;
>>>> +		goto err4;
>>>>  	}
>>>>  
>>>>  	dev_dbg(dev, "Samsung SoC SPI Driver loaded for Bus SPI-%d with %d Slaves attached\n",
>>>> @@ -1195,8 +1198,14 @@ static int s3c64xx_spi_probe(struct platform_device *pdev)
>>>>  					mem_res, (FIFO_LVL_MASK(sdd) >> 1) + 1,
>>>>  					sdd->rx_dma.dmach, sdd->tx_dma.dmach);
>>>>  
>>>> +	pm_runtime_mark_last_busy(dev);
>>>> +	pm_runtime_autosuspend(dev);
>>>
>>> There is a high chance that device will be suspended already at this
>>> point because pm_runtime_put() in setup. In most cases (when SPI is
>>> started) this won't do anything so we are back at first of my questions
>>> - shouldn't you update pm_runtime_put() calls?
>> Yes, these calls should be updated.
>>>
>>> Additionally (which is not related to your patch) shouldn't we
>>> pm_runtime_get() at some point in probe() to be sure that it won't be
>>> suspended to early?
>> Not 100% sure at this moment, I will check.
> Kernel documentation says:
> "Note, if the device may execute pm_runtime calls during the probe (such as
> if it is registers with a subsystem that may call back in) then the
> pm_runtime_get_sync() call paired with a pm_runtime_put() call will be
> appropriate to ensure that the device is not put back to sleep during the
> probe. This can happen with systems such as the network device layer."
> 
> I don't think this applies to SPI but I'm not expert enough to guarantee.
> At least no other SPI driver using runtime PM protects the probe function this way.
> Therefore I would dare to leave it as it is, especially as there don't seem
> to be any related known problems with SPI drivers.

But you know that these runtime callbacks will be executed anyway during
probe because what I mentioned earlier - setup calls get and put.
Additionally pm_runtime_enable() is called in the middle of probe, not
at the end. This means that already it is assumed probe in certain time
can handle runtime callbacks.

I think it is good opportunity to fix any remaining issues with runtime
PM in this driver.

Best regards,
Krzysztof

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