linux-kernel - Re: [PATCH 1/2] phy: marvell: comphy: Convert internal SMCC firmware return codes to errno

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Message-ID: <20200902174505.wuflkak6dv57jxw6@pali>
Date:   Wed, 2 Sep 2020 19:45:05 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Marek Behún <marek.behun@....cz>,
        Tomasz Maciej Nowak <tmn505@...il.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] phy: marvell: comphy: Convert internal SMCC firmware
 return codes to errno

On Wednesday 02 September 2020 19:20:29 Andrew Lunn wrote:
> On Wed, Sep 02, 2020 at 07:05:25PM +0200, Pali Rohár wrote:
> > On Wednesday 02 September 2020 19:00:10 Andrew Lunn wrote:
> > > > > > +	switch (ret) {
> > > > > > +	case SMCCC_RET_SUCCESS:
> > > > > > +		return 0;
> > > > > > +	case SMCCC_RET_NOT_SUPPORTED:
> > > > > > +		return -EOPNOTSUPP;
> > > > > > +	default:
> > > > > > +		return -EINVAL;
> > > > > > +	}
> > > > > >  }
> > > > > 
> > > > > Hi Pali
> > > > > 
> > > > > Maybe this should be a global helper translating SMCCC_RET_* into a
> > > > > standard errno value?
> > > > > 
> > > > > 	 Andrew
> > > > 
> > > > Hello Andrew!
> > > > 
> > > > Well, I'm not sure if some standard global helper is the correct way for
> > > > marvell comphy handler. It returns 0 for success and -1 on error when
> > > > handler is not supported.
> > > 
> > > No, i was meaning just 
> > > 
> > > switch (ret) {
> > > case SMCCC_RET_SUCCESS:
> > > 	return 0;
> > > case SMCCC_RET_NOT_SUPPORTED:
> > > 	return -EOPNOTSUPP;
> > > default:
> > > 	return -EINVAL;
> > > }
> > 
> > But this is not a complete generic helper. There are more generic SMCC
> > return codes and generic helper should define and translate all of them.
> 
> /*
>  * Return codes defined in ARM DEN 0070A
>  * ARM DEN 0070A is now merged/consolidated into ARM DEN 0028 C
>  */
> #define SMCCC_RET_SUCCESS			0
> #define SMCCC_RET_NOT_SUPPORTED			-1
> #define SMCCC_RET_NOT_REQUIRED			-2
> #define SMCCC_RET_INVALID_PARAMETER		-3

Routines can use also other custom return codes. These are IIRC just
standard defined.

> I only see problems with SMCCC_RET_NOT_REQUIRED and what value to use
> for it. Do you have any idea what is actually means? A parameter was
> passed which was not required? Or that the call itself is not
> required? Looking at the uses of it currently in the kernel, it does
> not seem to be an actual error. So maybe just return 0?

I'm not sure. That is why I wrote that larger discussion about generic
helper is needed. There are for sure people who understand SMC better
and have deep insight.

For Marvell comphy we cannot use return code -2 as success like 0.