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    SubjectRe: [PATCHv7 1/7] iommu/io-pgtable-arm: Add support to use system cache
    On Fri, Oct 30, 2020 at 02:53:08PM +0530, Sai Prakash Ranjan wrote:
    > Add a quirk IO_PGTABLE_QUIRK_SYS_CACHE to override the
    > attributes set in TCR for the page table walker when
    > using system cache.
    >
    > Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
    > ---
    > drivers/iommu/io-pgtable-arm.c | 7 ++++++-
    > include/linux/io-pgtable.h | 4 ++++
    > 2 files changed, 10 insertions(+), 1 deletion(-)
    >
    > diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
    > index a7a9bc08dcd1..a356caf1683a 100644
    > --- a/drivers/iommu/io-pgtable-arm.c
    > +++ b/drivers/iommu/io-pgtable-arm.c
    > @@ -761,7 +761,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
    >
    > if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
    > IO_PGTABLE_QUIRK_NON_STRICT |
    > - IO_PGTABLE_QUIRK_ARM_TTBR1))
    > + IO_PGTABLE_QUIRK_ARM_TTBR1 |
    > + IO_PGTABLE_QUIRK_SYS_CACHE))
    > return NULL;
    >
    > data = arm_lpae_alloc_pgtable(cfg);
    > @@ -773,6 +774,10 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
    > tcr->sh = ARM_LPAE_TCR_SH_IS;
    > tcr->irgn = ARM_LPAE_TCR_RGN_WBWA;
    > tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;
    > + } else if (cfg->quirks & IO_PGTABLE_QUIRK_SYS_CACHE) {
    > + tcr->sh = ARM_LPAE_TCR_SH_OS;
    > + tcr->irgn = ARM_LPAE_TCR_RGN_NC;
    > + tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;

    Given that this only applies in the case where then page-table walker is
    non-coherent, I think we'd be better off renaming the quirk to something
    like IO_PGTABLE_QUIRK_ARM_OUTER_WBWA and then rejecting it in the
    non-coherent case.

    > } else {
    > tcr->sh = ARM_LPAE_TCR_SH_OS;
    > tcr->irgn = ARM_LPAE_TCR_RGN_NC;
    > diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
    > index 4cde111e425b..86631f711e05 100644
    > --- a/include/linux/io-pgtable.h
    > +++ b/include/linux/io-pgtable.h
    > @@ -86,6 +86,9 @@ struct io_pgtable_cfg {
    > *
    > * IO_PGTABLE_QUIRK_ARM_TTBR1: (ARM LPAE format) Configure the table
    > * for use in the upper half of a split address space.
    > + *
    > + * IO_PGTABLE_QUIRK_SYS_CACHE: Override the attributes set in TCR for
    > + * the page table walker when using system cache.

    and then update this accordingly.

    Will

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