linux-kernel - Re: [PATCH 2/2] cxl/acpi: Use the ACPI CFMWS to create static decoder objects

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Date:   Tue, 15 Jun 2021 15:01:06 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Alison Schofield <alison.schofield@...el.com>
Cc:     Ben Widawsky <ben.widawsky@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        linux-cxl@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH 2/2] cxl/acpi: Use the ACPI CFMWS to create static decoder objects

On Tue, Jun 15, 2021 at 2:09 PM Alison Schofield
<alison.schofield@...el.com> wrote:
>
> Thanks for the review Dan...
>
> On Tue, Jun 15, 2021 at 11:48:43AM -0700, Dan Williams wrote:
> > [ add linu-acpi for variable length array question below ]
> >
> >
> > On Mon, Jun 14, 2021 at 3:57 PM Alison Schofield
> > <alison.schofield@...el.com> wrote:
> > >
> > > The ACPI CXL Early Discovery Table (CEDT) includes a list of CXL memory
> > > resources in CXL Fixed Memory Window Structures (CFMWS). Retrieve each
> > > CFMWS in the CEDT and add a cxl_decoder object to the root port (root0)
> > > for each memory resource.
> > >
> > > Signed-off-by: Alison Schofield <alison.schofield@...el.com>
> > > ---
> > >  drivers/cxl/acpi.c | 106 +++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 106 insertions(+)
> > >
> > > diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> > > index 16f60bc6801f..ac4b3e37e294 100644
> > > --- a/drivers/cxl/acpi.c
> > > +++ b/drivers/cxl/acpi.c
> > > @@ -8,8 +8,112 @@
> > >  #include <linux/pci.h>
> > >  #include "cxl.h"
> > >
> > > +/* Encode defined in CXL 2.0 8.2.5.12.7 HDM Decoder Control Register */
> > > +#define CFMWS_INTERLEAVE_WAYS(x)       (1 << (x)->interleave_ways)
> > > +#define CFMWS_INTERLEAVE_GRANULARITY(x)        ((x)->granularity + 8)
> > > +
> > > +/*
> > > + * CFMWS Restrictions mapped to CXL Decoder Flags
> > > + * Restrictions defined in CXL 2.0 ECN CEDT CFMWS
> > > + * Decoder Flags defined in CXL 2.0 8.2.5.12.7 HDM Decoder Control Register
> > > + */
> > > +#define CFMWS_TO_DECODE_TYPE2(x) ((x & ACPI_CEDT_CFMWS_RESTRICT_TYPE2) << 2)
> > > +#define CFMWS_TO_DECODE_TYPE3(x) ((x & ACPI_CEDT_CFMWS_RESTRICT_TYPE3) << 2)
> > > +#define CFMWS_TO_DECODE_RAM(x)   ((x & ACPI_CEDT_CFMWS_RESTRICT_VOLATILE) >> 2)
> > > +#define CFMWS_TO_DECODE_PMEM(x)         ((x & ACPI_CEDT_CFMWS_RESTRICT_PMEM) >> 2)
> > > +#define CFMWS_TO_DECODE_FIXED(x) (x & ACPI_CEDT_CFMWS_RESTRICT_FIXED)
> > > +
> > > +#define CFMWS_TO_DECODER_FLAGS(x) (CFMWS_TO_DECODE_TYPE2(x) | \
> > > +                                  CFMWS_TO_DECODE_TYPE3(x) | \
> > > +                                  CFMWS_TO_DECODE_RAM(x)   | \
> > > +                                  CFMWS_TO_DECODE_PMEM(x)  | \
> > > +                                  CFMWS_TO_DECODE_FIXED(x))
> >
> > I don't understand the approach taken above. It seems to assume that
> > the CXL_DECODER_F_* values are fixed. Those flag values are arbitrary
> > and mutable. There is no guarantee that today's CXL_DECODER_F_* values
> > match tomorrow's so I'd rather not have 2 places to check when / if
> > that happens.
> >
>
> Here's my next take - making the handling resilient.
> Not so sure on gracefulness. Open for suggestions.
>
> -#define CFMWS_TO_DECODE_TYPE2(x) ((x & ACPI_CEDT_CFMWS_RESTRICT_TYPE2) << 2)
> -#define CFMWS_TO_DECODE_TYPE3(x) ((x & ACPI_CEDT_CFMWS_RESTRICT_TYPE3) << 2)
> -#define CFMWS_TO_DECODE_RAM(x)   ((x & ACPI_CEDT_CFMWS_RESTRICT_VOLATILE) >> 2)
> -#define CFMWS_TO_DECODE_PMEM(x)         ((x & ACPI_CEDT_CFMWS_RESTRICT_PMEM) >> 2)
> -#define CFMWS_TO_DECODE_FIXED(x) (x & ACPI_CEDT_CFMWS_RESTRICT_FIXED)
> -
> -#define CFMWS_TO_DECODER_FLAGS(x) (CFMWS_TO_DECODE_TYPE2(x) | \
> -                                  CFMWS_TO_DECODE_TYPE3(x) | \
> -                                  CFMWS_TO_DECODE_RAM(x)   | \
> -                                  CFMWS_TO_DECODE_PMEM(x)  | \
> -                                  CFMWS_TO_DECODE_FIXED(x))
> +#define FLAG_TYPE2(x) \
> +       ((x & ACPI_CEDT_CFMWS_RESTRICT_TYPE2) ? CXL_DECODER_F_TYPE2 : 0)
> +#define FLAG_TYPE3(x) \
> +       ((x & ACPI_CEDT_CFMWS_RESTRICT_TYPE3) ? CXL_DECODER_F_TYPE3 : 0)
> +#define FLAG_RAM(x) \
> +       ((x & ACPI_CEDT_CFMWS_RESTRICT_VOLATILE) ? CXL_DECODER_F_RAM : 0)
> +#define FLAG_PMEM(x) \
> +       ((x & ACPI_CEDT_CFMWS_RESTRICT_PMEM) ? CXL_DECODER_F_PMEM : 0)
> +#define FLAG_FIXED(x) \
> +       ((x & ACPI_CEDT_CFMWS_RESTRICT_FIXED) ? CXL_DECODER_F_LOCK : 0)
> +
> +#define CFMWS_TO_DECODER_FLAGS(x) (FLAG_TYPE2(x) | FLAG_TYPE3(x) | \
> +                                  FLAG_RAM(x) | FLAG_PMEM(x)| FLAG_FIXED(x))

Hmm, why the macros? Just make CFMWS_TO_DECODER_FLAGS a proper function.

if (cfmws->restrictions & ACPI_CEDT_CFMWS_RESTRICT_TYPE2)
    flags |= CXL_DECODER_F_TYPE2;

...etc

Unless you foresee where macros were going to be reused somewhere else
I would just as soon open code them like above.