Re: [PATCH v5 3/6] riscv: errata: Add Andes alternative ports

[Conor Dooley]

On Mon, Dec 19, 2022 at 11:19:13AM +0000, Lad, Prabhakar wrote:
> Hi Conor,
> 
> Thank you for the review.
> 
> On Sat, Dec 17, 2022 at 9:19 PM Conor Dooley <conor@xxxxxxxxxx> wrote:
> >
> > On Mon, Dec 12, 2022 at 11:55:02AM +0000, Prabhakar wrote:
> > > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> > >
> > > Add required ports of the Alternative scheme for Andes CPU cores.
> > >
> > > I/O Coherence Port (IOCP) provides an AXI interface for connecting external
> > > non-caching masters, such as DMA controllers. IOCP is a specification
> > > option and is disabled on the Renesas RZ/Five SoC due to this reason cache
> > > management needs a software workaround.
> > >
> > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> > > ---
> > > v4 -> v5
> > > * Sorted the Kconfig/Makefile/Switch based on Core name
> > > * Added a comments
> > > * Introduced RZFIVE_SBI_EXT_IOCP_SW_WORKAROUND SBI EXT ID to check if
> > >   CMO needs to be applied. Is there a way we can access the DTB while patching
> > >   as we can drop this SBI EXT ID and add a DT property instead for cmo?
> > >
> > > RFC v3 -> v4
> > > * New patch
> > > ---
> > >  arch/riscv/Kconfig.erratas           | 22 +++++++
> > >  arch/riscv/errata/Makefile           |  1 +
> > >  arch/riscv/errata/andes/Makefile     |  1 +
> > >  arch/riscv/errata/andes/errata.c     | 93 ++++++++++++++++++++++++++++
> > >  arch/riscv/include/asm/alternative.h |  3 +
> > >  arch/riscv/include/asm/errata_list.h |  5 ++
> > >  arch/riscv/kernel/alternative.c      |  5 ++
> > >  7 files changed, 130 insertions(+)
> > >  create mode 100644 arch/riscv/errata/andes/Makefile
> > >  create mode 100644 arch/riscv/errata/andes/errata.c
> > >
> > > diff --git a/arch/riscv/Kconfig.erratas b/arch/riscv/Kconfig.erratas
> > > index 69621ae6d647..f0f0c1abd52b 100644
> > > --- a/arch/riscv/Kconfig.erratas
> > > +++ b/arch/riscv/Kconfig.erratas
> > > @@ -1,5 +1,27 @@
> > >  menu "CPU errata selection"
> > >
> > > +config ERRATA_ANDES
> > > +     bool "Andes AX45MP errata"
> > > +     depends on !XIP_KERNEL
> > > +     select RISCV_ALTERNATIVE
> > > +     help
> > > +       All Andes errata Kconfig depend on this Kconfig. Disabling
> > > +       this Kconfig will disable all Andes errata. Please say "Y"
> > > +       here if your platform uses Andes CPU cores.
> > > +
> > > +       Otherwise, please say "N" here to avoid unnecessary overhead.
> > > +
> > > +config ERRATA_ANDES_CMO
> > > +     bool "Apply Andes cache management errata"
> > > +     depends on ERRATA_ANDES && MMU && ARCH_R9A07G043
> > > +     select RISCV_DMA_NONCOHERENT
> > > +     default y
> > > +     help
> > > +       This will apply the cache management errata to handle the
> > > +       non-standard handling on non-coherent operations on Andes cores.
> > > +
> > > +       If you don't know what to do here, say "Y".
> > > +
> > >  config ERRATA_SIFIVE
> > >       bool "SiFive errata"
> > >       depends on !XIP_KERNEL
> > > diff --git a/arch/riscv/errata/Makefile b/arch/riscv/errata/Makefile
> > > index a1055965fbee..6f1c693af92d 100644
> > > --- a/arch/riscv/errata/Makefile
> > > +++ b/arch/riscv/errata/Makefile
> > > @@ -1,2 +1,3 @@
> > > +obj-$(CONFIG_ERRATA_ANDES) += andes/
> > >  obj-$(CONFIG_ERRATA_SIFIVE) += sifive/
> > >  obj-$(CONFIG_ERRATA_THEAD) += thead/
> > > diff --git a/arch/riscv/errata/andes/Makefile b/arch/riscv/errata/andes/Makefile
> > > new file mode 100644
> > > index 000000000000..2d644e19caef
> > > --- /dev/null
> > > +++ b/arch/riscv/errata/andes/Makefile
> > > @@ -0,0 +1 @@
> > > +obj-y += errata.o
> > > diff --git a/arch/riscv/errata/andes/errata.c b/arch/riscv/errata/andes/errata.c
> > > new file mode 100644
> > > index 000000000000..3d04f15df8d5
> > > --- /dev/null
> > > +++ b/arch/riscv/errata/andes/errata.c
> > > @@ -0,0 +1,93 @@
> > > +// SPDX-License-Identifier: GPL-2.0-only
> > > +/*
> > > + * Erratas to be applied for Andes CPU cores
> > > + *
> > > + *  Copyright (C) 2022 Renesas Electronics Corporation.
> > > + *
> > > + * Author: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> > > + */
> > > +
> > > +#include <linux/kernel.h>
> > > +#include <linux/module.h>
> > > +
> > > +#include <asm/alternative.h>
> > > +#include <asm/cacheflush.h>
> > > +#include <asm/errata_list.h>
> > > +#include <asm/patch.h>
> > > +#include <asm/sbi.h>
> > > +#include <asm/vendorid_list.h>
> > > +
> > > +#define ANDESTECH_AX45MP_MARCHID     0x8000000000008a45UL
> > > +#define ANDESTECH_AX45MP_MIMPID              0x500UL
> > > +#define ANDESTECH_SBI_EXT_ANDES              0x0900031E
> > > +
> > > +#define RZFIVE_SBI_EXT_IOCP_SW_WORKAROUND    0
> > > +
> > > +static long ax45mp_iocp_sw_workaround(void)
> > > +{
> > > +     struct sbiret ret;
> > > +
> > > +     ret = sbi_ecall(ANDESTECH_SBI_EXT_ANDES, RZFIVE_SBI_EXT_IOCP_SW_WORKAROUND,
> > > +                     0, 0, 0, 0, 0, 0);
> >
> > Seeing as you need a new version for some of the other bits, I think it
> > would be good to add a minor comment here somewhere (be it here or the
> > commit message) that links to the SBI specs for this.
> > I think this looks pretty good though.
> Sure I'll add a comment here.
> 
> I was wondering if we can get rid of this vendor specific extension
> here if we get access to the DT here (for example having a DT property
> which would indicate if IOCP CMO should be applied or not). Do you
> think that would be good approach?  ATM we dont have a pointer here
> for FDT whie early patching.

I dunno. I think it is fine to use the ECALL to be honest - I'd rather
that than a property that someone may omit.

That said, for the cache management stuff we are gonna need for
PolarFire SoC, we will need to have info from the DT AFAICT - marchid
etc are all set to zero on our platform so cannot be used.

I was thinking about using the compatible instead, but...
we've not tried to "forward"-port our stuff from 5.15 yet as we have
not yet completed testing testing on our vendor tree (and need some PCI
changes accepted upstream first anyway), as a result I have not looked
into what's needed there for use with alternatives. We've been using a
pre-alternatives version of that patchset from around the 5.15
development point in time instead.

Thanks,
Conor.

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