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From:   <ilialin@codeaurora.org>
To:     "'Sudeep Holla'" <sudeep.holla@arm.com>
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Subject: RE: [PATCH v12 1/2] cpufreq: Add Kryo CPU scaling driver
Date:   Thu, 24 May 2018 17:10:32 +0300
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Thank you for the explanation. However, could you suggest, which =
condition should I check then? Device tree?

> -----Original Message-----
> From: Sudeep Holla <sudeep.holla@arm.com>
> Sent: Thursday, May 24, 2018 17:01
> To: ilialin@codeaurora.org; vireshk@kernel.org; nm@ti.com;
> sboyd@kernel.org; robh@kernel.org; mark.rutland@arm.com;
> rjw@rjwysocki.net
> Cc: Sudeep Holla <sudeep.holla@arm.com>; linux-pm@vger.kernel.org;
> devicetree@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v12 1/2] cpufreq: Add Kryo CPU scaling driver
>=20
>=20
>=20
> On 24/05/18 14:03, ilialin@codeaurora.org wrote:
> >
> >
>=20
> [...]
>=20
> >>> +
> >>> +	ret =3D PTR_ERR_OR_ZERO(platform_device_register_simple(
> >>> +		"qcom-cpufreq-kryo", -1, NULL, 0));
> >>
> >>
> >> You simply can't do this unconditionally here. This will blow up on
> >> platforms where this driver is not supposed to work. The probe will
> >> be called on non- QCOM or non-Kryo QCOM platforms and I reckon it
> >> will crash trying to execute something in qcom_smem_get.
> >
> > What do you mean by 'unconditionally'?
>=20
> Why should you even add/register a device "qcom-cpufreq-kryo" on other
> platforms. Drivers can get registered, but only devices that are =
present or
> required by the platform need to be registered.
>=20
> > The driver depends on the smem and nvmem drivers, which depend on
> ARCH_QCOM:
> >  +	depends on QCOM_QFPROM
> >  +	depends on QCOM_SMEM
> >
>=20
> Sure, but we have something called single image for all ARM64 =
platforms.
> May be QCOM still used to tweeking config to build binary for your =
particular
> mobile platform but the distro kernel need single binary to work on =
all
> platforms. We have moved far away from platform specific builds long =
back
> now IIRC.
>=20
> > And if SMEM read in the probe returns something other than Kryo, it =
will
> exit.
> >
>=20
> Check what this driver does ?
>=20
> 	msm_id =3D qcom_smem_get(QCOM_SMEM_HOST_ANY,
> MSM_ID_SMEM, &len);
> 	msm_id++;
> 	switch ((enum _msm_id)*msm_id)
>=20
> I think it *will and should* crash here ? You need to check the return =
value
> for sure. But since qcom_smem_get return -EPROBE_DEFER, we keep
> retrying even on non QCOM platforms which is something I would like to
> avoid.
>=20
> Therefore that's not the main concern. Why do I have to see =
"qcom-cpufreq-
> kryo" device registered on my non QCOM platform ?
>=20
> --
> Regards,
> Sudeep