Messages in this thread | | | Date | Thu, 12 Oct 2023 14:43:18 +0200 | Subject | Re: [PATCH v2 1/2] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO | From | Clément Léger <> |
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On 01/10/2023 12:34, Jisheng Zhang wrote: > Previously, we use alternative mechanism to dynamically patch > the CMO operations for THEAD C906/C910 during boot for performance > reason. But as pointed out by Arnd, "there is already a significant > cost in accessing the invalidated cache lines afterwards, which is > likely going to be much higher than the cost of an indirect branch". > And indeed, there's no performance difference with GMAC and EMMC per > my test on Sipeed Lichee Pi 4A board. > > Use riscv_nonstd_cache_ops for THEAD C906/C910 CMO to simplify > the alternative code, and to acchieve Arnd's goal -- "I think > moving the THEAD ops at the same level as all nonstandard operations > makes sense, but I'd still leave CMO as an explicit fast path that > avoids the indirect branch. This seems like the right thing to do both > for readability and for platforms on which the indirect branch has a > noticeable overhead." > > Signed-off-by: Jisheng Zhang <jszhang@kernel.org> > Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com> > --- > arch/riscv/Kconfig.errata | 1 + > arch/riscv/errata/thead/errata.c | 75 +++++++++++++++++++++++++++- > arch/riscv/include/asm/errata_list.h | 50 +++---------------- > 3 files changed, 80 insertions(+), 46 deletions(-) > > diff --git a/arch/riscv/Kconfig.errata b/arch/riscv/Kconfig.errata > index 566bcefeab50..d7972914f9de 100644 > --- a/arch/riscv/Kconfig.errata > +++ b/arch/riscv/Kconfig.errata > @@ -78,6 +78,7 @@ config ERRATA_THEAD_CMO > bool "Apply T-Head cache management errata" > depends on ERRATA_THEAD && MMU > select RISCV_DMA_NONCOHERENT > + select RISCV_NONSTANDARD_CACHE_OPS > default y > help > This will apply the cache management errata to handle the > diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c > index 0554ed4bf087..3fefeb1b456e 100644 > --- a/arch/riscv/errata/thead/errata.c > +++ b/arch/riscv/errata/thead/errata.c > @@ -12,8 +12,10 @@ > #include <asm/alternative.h> > #include <asm/cacheflush.h> > #include <asm/cpufeature.h> > +#include <asm/dma-noncoherent.h> > #include <asm/errata_list.h> > #include <asm/hwprobe.h> > +#include <asm/io.h> > #include <asm/patch.h> > #include <asm/vendorid_list.h> > > @@ -33,6 +35,75 @@ static bool errata_probe_pbmt(unsigned int stage, > return false; > } > > +/* > + * dcache.ipa rs1 (invalidate, physical address) > + * | 31 - 25 | 24 - 20 | 19 - 15 | 14 - 12 | 11 - 7 | 6 - 0 | > + * 0000001 01010 rs1 000 00000 0001011 > + * dache.iva rs1 (invalida, virtual address)
Small typo here: invalidate instead of invalida
Thanks,
Clément
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