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Message-ID: <ZHdmnfJvF1N5rgvx@xhacker>
Date: Wed, 31 May 2023 23:24:13 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: Conor Dooley <conor.dooley@...rochip.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH 4/6] riscv: mm: pass noncoherent or not to
riscv_noncoherent_supported()
On Mon, May 29, 2023 at 12:13:10PM +0100, Conor Dooley wrote:
> Hey Jisheng,
Hi Conor,
>
> On Sat, May 27, 2023 at 12:59:56AM +0800, Jisheng Zhang wrote:
> > We will soon take different actions by checking the HW is noncoherent
> > or not, I.E ZICBOM/ERRATA_THEAD_CMO or not.
> >
> > Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
> > ---
> > arch/riscv/errata/thead/errata.c | 19 +++++++++++--------
> > arch/riscv/include/asm/cacheflush.h | 4 ++--
> > arch/riscv/kernel/setup.c | 6 +++++-
> > arch/riscv/mm/dma-noncoherent.c | 10 ++++++----
> > 4 files changed, 24 insertions(+), 15 deletions(-)
> >
> > diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> > index be84b14f0118..c192b80a5166 100644
> > --- a/arch/riscv/errata/thead/errata.c
> > +++ b/arch/riscv/errata/thead/errata.c
> > @@ -36,21 +36,24 @@ static bool errata_probe_pbmt(unsigned int stage,
> > static bool errata_probe_cmo(unsigned int stage,
> > unsigned long arch_id, unsigned long impid)
> > {
> > - if (!IS_ENABLED(CONFIG_ERRATA_THEAD_CMO))
> > - return false;
> > -
> > - if (arch_id != 0 || impid != 0)
> > - return false;
> > + bool cmo;
> >
> > if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
> > return false;
> >
> > + if (IS_ENABLED(CONFIG_ERRATA_THEAD_CMO) &&
> > + (arch_id == 0 && impid == 0))
> > + cmo = true;
> > + else
> > + cmo = false;
> > +
> > if (stage == RISCV_ALTERNATIVES_BOOT) {
> > - riscv_cbom_block_size = L1_CACHE_BYTES;
> > - riscv_noncoherent_supported();
> > + if (cmo)
> > + riscv_cbom_block_size = L1_CACHE_BYTES;
> > + riscv_noncoherent_supported(cmo);
> > }
> >
> > - return true;
> > + return cmo;
>
> I don't really understand the changes that you are making to this
> function, so that is tries really hard to call
> riscv_noncoherent_supported(). Why do we need to always call the function
> in the erratum's probe function, if the erratum is not detected, given
In one unified kernel Image, to support both coherent and noncoherent
platforms(currently, either T-HEAD CMO or ZICBOM), we need to let the
kmalloc meet both cases, specifically, ARCH_DMA_MINALIGN aligned.
Once we know the underlying HW is coherent, I.E neither T-HEAD CMO nor
ZICBOM, we need to notice kmalloc we are safe to reduce the alignment
to 1. The notice action is done in patch 5:
+ } else {
+ dma_cache_alignment = 1;
> that riscv_noncoherent_supported() is called immediately after
> apply_boot_alternatives() in setup_arch()?
>
> > }
> >
> > static bool errata_probe_pmu(unsigned int stage,
> > diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
> > index 8091b8bf4883..9d056c9b625a 100644
> > --- a/arch/riscv/include/asm/cacheflush.h
> > +++ b/arch/riscv/include/asm/cacheflush.h
> > @@ -54,9 +54,9 @@ extern unsigned int riscv_cboz_block_size;
> > void riscv_init_cbo_blocksizes(void);
> >
> > #ifdef CONFIG_RISCV_DMA_NONCOHERENT
> > -void riscv_noncoherent_supported(void);
> > +void riscv_noncoherent_supported(bool cmo);
>
> I think it would "read better" if you renamed this variable to
> "have_cmo".
>
> > #else
> > -static inline void riscv_noncoherent_supported(void) {}
> > +static inline void riscv_noncoherent_supported(bool cmo) {}
> > #endif
> >
> > /*
> > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> > index 36b026057503..565f3e20169b 100644
> > --- a/arch/riscv/kernel/setup.c
> > +++ b/arch/riscv/kernel/setup.c
> > @@ -264,6 +264,7 @@ static void __init parse_dtb(void)
> >
> > void __init setup_arch(char **cmdline_p)
> > {
> > + bool cmo;
> > parse_dtb();
> > setup_initial_init_mm(_stext, _etext, _edata, _end);
> >
> > @@ -298,7 +299,10 @@ void __init setup_arch(char **cmdline_p)
> > apply_boot_alternatives();
> > if (IS_ENABLED(CONFIG_RISCV_ISA_ZICBOM) &&
> > riscv_isa_extension_available(NULL, ZICBOM))
> > - riscv_noncoherent_supported();
> > + cmo = true;
> > + else
> > + cmo = false;
> > + riscv_noncoherent_supported(cmo);
>
> As a nit, could you put a newline before the call to
> riscv_noncoherent_supported()?
>
> > }
> >
> > static int __init topology_init(void)
> > diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c
> > index d51a75864e53..0e172e2b4751 100644
> > --- a/arch/riscv/mm/dma-noncoherent.c
> > +++ b/arch/riscv/mm/dma-noncoherent.c
> > @@ -72,9 +72,11 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
> > dev->dma_coherent = coherent;
> > }
> >
> > -void riscv_noncoherent_supported(void)
> > +void riscv_noncoherent_supported(bool cmo)
> > {
> > - WARN(!riscv_cbom_block_size,
> > - "Non-coherent DMA support enabled without a block size\n");
> > - noncoherent_supported = true;
> > + if (cmo) {
> > + WARN(!riscv_cbom_block_size,
> > + "Non-coherent DMA support enabled without a block size\n");
> > + noncoherent_supported = true;
> > + }
>
> The other places that we do a WARN() because of screwed up devicetrees
> for CMO things, we do a WARN_TAINT(CPU_OUT_OF_SPEC). Should we do the
> same here too?
>
> Cheers,
> Conor.
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