Re: [PATCH RFC 2/2] soc: Add a basic ACPI generic driver

[John Garry]

On 28/01/2020 15:20, Sudeep Holla wrote:
> (commenting on other parts though I am not sure if we want to add this
> despite it being deprecated)
>
> On Tue, Jan 28, 2020 at 07:14:19PM +0800, John Garry wrote:
> > Add a generic driver for platforms which populate their ACPI PPTT
> > processor package ID Type Structure according to suggestion in the ACPI
> > spec - see ACPI 6.2, section 5.2.29.3 ID structure Type 2.
> >
> > The soc_id is from member LEVEL_2_ID.
> >
> > For this, we need to use a whitelist of platforms which are known to
> > populate the structure as suggested.
> >
> > For now, only the vendor and soc_id fields are exposed.
> >
> > Signed-off-by: John Garry<john.garry@xxxxxxxxxx>
> > ---
> >   drivers/soc/Makefile       |   1 +
> >   drivers/soc/acpi_generic.c | 102 +++++++++++++++++++++++++++++++++++++
> >   2 files changed, 103 insertions(+)
> >   create mode 100644 drivers/soc/acpi_generic.c
> >
> > diff --git a/drivers/soc/Makefile b/drivers/soc/Makefile
> > index 8b49d782a1ab..2a59a30a22cd 100644
> > --- a/drivers/soc/Makefile
> > +++ b/drivers/soc/Makefile
> > @@ -3,6 +3,7 @@
> >   # Makefile for the Linux Kernel SOC specific device drivers.
> >   #
> >
> > +obj-$(CONFIG_ACPI_PPTT)		+= acpi_generic.o
> >   obj-$(CONFIG_ARCH_ACTIONS)	+= actions/
> >   obj-$(CONFIG_SOC_ASPEED)	+= aspeed/
> >   obj-$(CONFIG_ARCH_AT91)		+= atmel/
> > diff --git a/drivers/soc/acpi_generic.c b/drivers/soc/acpi_generic.c
> > new file mode 100644
> > index 000000000000..34a1f5f8e063
> > --- /dev/null
> > +++ b/drivers/soc/acpi_generic.c
> > @@ -0,0 +1,102 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c) John Garry,john.garry@xxxxxxxxxx
> > + */
> > +
> > +#define pr_fmt(fmt) "SOC ACPI GENERIC: " fmt
> > +
> > +#include <linux/acpi.h>
> > +#include <linux/sys_soc.h>
> > +
> > +/*
> > + * Known platforms that fill in PPTT package ID structures according to
> > + * ACPI spec examples, that being:
> > + * - Custom driver attribute is in ID Type Structure VENDOR_ID member
> > + * - SoC id is in ID Type Structure LEVEL_2_ID member
> > + *    See ACPI SPEC 6.2 Table 5-154 for PPTT ID Type Structure
> > + */
> > +static struct acpi_platform_list plat_list[] = {
> > +	{"HISI  ", "HIP08   ", 0, ACPI_SIG_PPTT, all_versions},

Hi Sudeep,

> What do you want to match this ? The same silicon can end up with
> different OEMs and this list just blows up soon for single SoC if
> used by different OEM/ODMs. I assume we get all the required info
> from the Type 2 table entry and hence can just rely on that. If
> PPTT has type 2 entry, just initialise this soc driver and expose
> the relevant information from the table entry.

As before, the LEVEL_1_ID and LEVEL_2_ID table members are too open to 
interpretation in the spec to generate a consistent form soc_id and 
family_id for all platforms.

As such, I was trying to limit to known PPTT implementations and how 
they should be interpreted. Obviously that's *far* from ideal.

So what's your idea? Just always put LEVEL_1_ID and LEVEL_2_ID in soc 
driver family_id and soc_id fields, respectively?

Thanks,
John