linux-kernel - Re: [PATCH v2] extcon: extcon-axp288: use low level P-Unit semaphore lock for axp288 register accesses

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Date:   Thu, 16 Sep 2021 08:51:42 +0200
From:   Fabio Aiuto <fabioaiuto83@...il.com>
To:     Chanwoo Choi <cwchoi00@...il.com>
Cc:     Chanwoo Choi <cw00.choi@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] extcon: extcon-axp288: use low level P-Unit semaphore
 lock for axp288 register accesses

Hello Chanwoo,

On Thu, Sep 16, 2021 at 02:12:26AM +0900, Chanwoo Choi wrote:
> Hi,
> 
> On 21. 9. 10. 오후 4:34, Fabio Aiuto wrote:
> > use low level P-Unit semaphore lock for axp288 register
> > accesses directly and for more than one access a time,
> > to reduce the number of times this semaphore is locked
> > and released which is an expensive operation.
> > 
> > i2c-bus to the XPower is shared between the kernel and the
> > SoCs P-Unit. The P-Unit has a semaphore wich the kernel must
> > lock for axp288 register accesses. When the P-Unit semaphore
> > is locked CPU and GPU power states cannot change or the system
> > will freeze.
> > 
> > The P-Unit semaphore lock is already managed inside the regmap
> > access logic, but for each access the semaphore is locked and
> > released. So use directly iosf_mbi_(un)block_punit_i2c_access(),
> > we are safe in doing so because nested calls to the same
> > semaphore are turned to nops.
> > 
> > Suggested-by: Hans de Goede <hdegoede@...hat.com>
> > Reviewed-by: Hans de Goede <hdegoede@...hat.com>
> > Tested-by: Hans de Goede <hdegoede@...hat.com>
> > Signed-off-by: Fabio Aiuto <fabioaiuto83@...il.com>
> > ---
> > Changes in v2:
> > 	- add a new depends on in Kconfig
> > 	- add Tested-by Reviewed-by tags
> >   drivers/extcon/Kconfig         |  2 +-
> >   drivers/extcon/extcon-axp288.c | 14 ++++++++++++++
> >   2 files changed, 15 insertions(+), 1 deletion(-)

<snip>

> >   #define PS_STAT_VBUS_TRIGGER		BIT(0)
> > @@ -215,6 +216,8 @@ static int axp288_handle_chrg_det_event(struct axp288_extcon_info *info)
> >   	unsigned int cable = info->previous_cable;
> >   	bool vbus_attach = false;
> > +	iosf_mbi_block_punit_i2c_access();
> 
> You have to check the return value of iosf_mbi_block_punit_i2c_access()

ok will send a v2, with all the fixes you pointed out.

<snip>

> 
> -- 
> Best Regards,
> Samsung Electronics
> Chanwoo Choi

thank you,

fabio