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Date:   Fri, 1 May 2020 16:57:29 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Steven Price <steven.price@....com>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <Catalin.Marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <Mark.Rutland@....com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        "Harb Abdulhamid (harb@...erecomputing.com)" 
        <harb@...erecomputing.com>
Subject: Re: [PATCH 5/5] arm/arm64: smccc: Add ARCH_SOC_ID support

Hi Steve,

Thanks for taking a reviewing these patches.

On Fri, May 01, 2020 at 04:07:39PM +0100, Steven Price wrote:
> On 30/04/2020 12:48, Sudeep Holla wrote:
> > SMCCC v1.2 adds a new optional function SMCCC_ARCH_SOC_ID to obtain a
> > SiP defined SoC identification value. Add support for the same.
> >
> > Also using the SoC bus infrastructure, let us expose the platform
> > specific SoC atrributes under sysfs. We also provide custom sysfs for
> > the vendor ID as JEP-106 bank and identification code.
> >
> > Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> > ---
> >   drivers/firmware/psci/Makefile |   2 +-
> >   drivers/firmware/psci/soc_id.c | 148 +++++++++++++++++++++++++++++++++
> >   include/linux/arm-smccc.h      |   5 ++
> >   3 files changed, 154 insertions(+), 1 deletion(-)
> >   create mode 100644 drivers/firmware/psci/soc_id.c
> >
> > diff --git a/drivers/firmware/psci/Makefile b/drivers/firmware/psci/Makefile
> > index 1956b882470f..c0b0c9ca57e4 100644
> > --- a/drivers/firmware/psci/Makefile
> > +++ b/drivers/firmware/psci/Makefile
> > @@ -1,4 +1,4 @@
> >   # SPDX-License-Identifier: GPL-2.0
> >   #
> > -obj-$(CONFIG_ARM_PSCI_FW)	+= psci.o
> > +obj-$(CONFIG_ARM_PSCI_FW)	+= psci.o soc_id.o
> >   obj-$(CONFIG_ARM_PSCI_CHECKER)	+= psci_checker.o
> > diff --git a/drivers/firmware/psci/soc_id.c b/drivers/firmware/psci/soc_id.c
> > new file mode 100644
> > index 000000000000..820f69dad7f5
> > --- /dev/null
> > +++ b/drivers/firmware/psci/soc_id.c
> > @@ -0,0 +1,148 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright 2020 Arm Limited
> > + */
> > +
> > +#include <linux/arm-smccc.h>
> > +#include <linux/bitfield.h>
> > +#include <linux/device.h>
> > +#include <linux/module.h>
> > +#include <linux/kernel.h>
> > +#include <linux/slab.h>
> > +#include <linux/sys_soc.h>
> > +
> > +#define SOCID_JEP106_BANK_IDX_MASK	GENMASK(30, 24)
> > +#define SOCID_JEP106_ID_CODE_MASK	GENMASK(23, 16)
> > +#define SOCID_IMP_DEF_SOC_ID_MASK	GENMASK(15, 0)
> > +#define JEP106_BANK_IDX(x)	(u8)(FIELD_GET(SOCID_JEP106_BANK_IDX_MASK, (x)))
> > +#define JEP106_ID_CODE(x)	(u8)(FIELD_GET(SOCID_JEP106_ID_CODE_MASK, (x)))
> > +#define IMP_DEF_SOC_ID(x)	(u16)(FIELD_GET(SOCID_IMP_DEF_SOC_ID_MASK, (x)))
> > +
> > +static int soc_id_version;
> > +static struct soc_device *soc_dev;
> > +static struct soc_device_attribute *soc_dev_attr;
> > +
> > +static int smccc_map_error_codes(unsigned long a0)
> > +{
> > +	if (a0 == SMCCC_RET_INVALID_PARAMETER)
> > +		return -EINVAL;
> > +	if (a0 == SMCCC_RET_NOT_SUPPORTED)
> > +		return -EOPNOTSUPP;
> > +	return 0;
>
> It seems odd to special case just those errors. While they are the only
> errors we expect, any result with the high bit set is an error (arguably a
> bug in the firmware) so should really cause an error return.
>

I agree and happy to change it. I too thought about the same for a while and
they left it for review time to finalise 😄 

> > +}
> > +
> > +static int smccc_soc_id_support_check(void)
> > +{
> > +	struct arm_smccc_res res;
> > +
> > +	if (arm_smccc_1_1_get_conduit() == SMCCC_CONDUIT_NONE) {
> > +		pr_err("%s: invalid SMCCC conduit\n", __func__);
> > +		return -EOPNOTSUPP;
> > +	}
> > +
> > +	arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
> > +			     ARM_SMCCC_ARCH_SOC_ID, &res);
> > +
> > +	return smccc_map_error_codes(res.a0);
> > +}
> > +
> > +static ssize_t
> > +jep106_cont_bank_code_show(struct device *dev, struct device_attribute *attr,
> > +			   char *buf)
> > +{
> > +	return sprintf(buf, "%02x\n", JEP106_BANK_IDX(soc_id_version) + 1);
> > +}
> > +
> > +static DEVICE_ATTR_RO(jep106_cont_bank_code);
> > +
> > +static ssize_t
> > +jep106_identification_code_show(struct device *dev,
> > +				struct device_attribute *attr, char *buf)
> > +{
> > +	return sprintf(buf, "%02x\n", JEP106_ID_CODE(soc_id_version) & 0x7F);
>
> It seems odd to have the mask defined to include a bit that is then always
> masked off. From the spec I presume this is a parity bit, but it would be
> good to have a comment explaining this.
>

Sure, actually I can to make it part of the macro itself and add a note
there.

> > +}
> > +
> > +static DEVICE_ATTR_RO(jep106_identification_code);
> > +
> > +static struct attribute *jep106_id_attrs[] = {
> > +	&dev_attr_jep106_cont_bank_code.attr,
> > +	&dev_attr_jep106_identification_code.attr,
> > +	NULL
> > +};
> > +
> > +ATTRIBUTE_GROUPS(jep106_id);
> > +
> > +static int __init smccc_soc_init(void)
> > +{
> > +	struct device *dev;
> > +	int ret, soc_id_rev;
> > +	struct arm_smccc_res res;
> > +	static char soc_id_str[8], soc_id_rev_str[12];
> > +
> > +	if (arm_smccc_get_version() < ARM_SMCCC_VERSION_1_2)
> > +		return 0;
>
> NIT: Do we actually need to check the version here - or would probing
> ARM_SMCCC_ARCH_FEATURES_FUNC_ID as is done below sufficient? I'm not aware
> of this relying on any new semantics that v1.2 added.
>

It should be sufficient, but I am trying to avoid raising error if it is
not SMCCC v1.2+, hence the return 0.

> > +
> > +	ret = smccc_soc_id_support_check();
> > +	if (ret)
> > +		return ret;
>
> This seems odd - if the version is <v1.2 then we return 0. But if it's >=1.2
> but doesn't support SOC_ID then it's an error return?
>

You are right, I see that now. I can flag a note/info and return 0.

--
Regards,
Sudeep

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