linux-kernel - RE: [PATCH v2 04/12] i2c: riic: Use pm_runtime_resume_and

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Message-ID:
 <TY3PR01MB1134643285CAA6D02292037FC86DA2@TY3PR01MB11346.jpnprd01.prod.outlook.com>
Date: Mon, 8 Jul 2024 05:36:50 +0000
From: Biju Das <biju.das.jz@...renesas.com>
To: Andi Shyti <andi.shyti@...nel.org>, Claudiu.Beznea
	<claudiu.beznea@...on.dev>
CC: Chris Brandt <Chris.Brandt@...esas.com>, "robh@...nel.org"
	<robh@...nel.org>, "krzk+dt@...nel.org" <krzk+dt@...nel.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>, "geert+renesas@...der.be"
	<geert+renesas@...der.be>, "magnus.damm@...il.com" <magnus.damm@...il.com>,
	"mturquette@...libre.com" <mturquette@...libre.com>, "sboyd@...nel.org"
	<sboyd@...nel.org>, "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
	"wsa+renesas@...g-engineering.com" <wsa+renesas@...g-engineering.com>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>, Claudiu Beznea
	<claudiu.beznea.uj@...renesas.com>
Subject: RE: [PATCH v2 04/12] i2c: riic: Use pm_runtime_resume_and_get()

Hi Andi and Claudiu,

> -----Original Message-----
> From: Andi Shyti <andi.shyti@...nel.org>
> Sent: Thursday, July 4, 2024 11:43 PM
> Subject: Re: [PATCH v2 04/12] i2c: riic: Use pm_runtime_resume_and_get()
> 
> Hi Claudiu,
> 
> > diff --git a/drivers/i2c/busses/i2c-riic.c
> > b/drivers/i2c/busses/i2c-riic.c index 83e4d5e14ab6..002b11b020fa
> > 100644
> > --- a/drivers/i2c/busses/i2c-riic.c
> > +++ b/drivers/i2c/busses/i2c-riic.c
> > @@ -113,6 +113,8 @@ struct riic_irq_desc {
> >  	char *name;
> >  };
> >
> > +static const char * const riic_rpm_err_msg = "Failed to runtime
> > +resume";
> 
> Please, don't do this. Much clearer to write the message explicitly.
> 
> > +
> >  static inline void riic_writeb(struct riic_dev *riic, u8 val, u8
> > offset)  {
> >  	writeb(val, riic->base + riic->info->regs[offset]); @@ -133,10
> > +135,14 @@ static int riic_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
> >  	struct riic_dev *riic = i2c_get_adapdata(adap);
> >  	struct device *dev = adap->dev.parent;
> >  	unsigned long time_left;
> > -	int i;
> > +	int i, ret;
> >  	u8 start_bit;
> >
> > -	pm_runtime_get_sync(dev);
> > +	ret = pm_runtime_resume_and_get(dev);
> 
> In principle I like the error message to be always checked and I will always approve it. Whenever
> there is a return value, even when we are sure it's always '0', it needs to be checked.
> 
> I had lots of discussions in the past about this topic but I haven't always found support. I'd love
> to have the ack from a renesas maintainer here.
> 
> > +	if (ret) {

Checking ret will lead to imbalance. It should be ret < 0 as ret = 1 corresponds to RPM_ACTIVE
and the API does not call put() when ret = 1; see [1] and [2]

[1] https://elixir.bootlin.com/linux/v6.10-rc6/source/drivers/base/power/runtime.c#L778

[2] https://elixir.bootlin.com/linux/v6.10-rc6/source/include/linux/pm_runtime.h#L431


Another question, pm_runtime_put [3] can also return error, don't we need to propagate that as well to caller??

[3] https://elixir.bootlin.com/linux/v6.10-rc6/source/drivers/base/power/runtime.c#L1086

Cheers,
Biju