Re: [RFC PATCH v1] iommu/arm-smmu: Allow domains to choose a context bank

[Rob Clark]

On Tue, Jan 28, 2020 at 2:34 PM Jordan Crouse <jcrouse@xxxxxxxxxxxxxx> wrote:
>
> Domains which are being set up for split pagetables usually want to be
> on a specific context bank for hardware reasons. Force the context
> bank for domains with the split-pagetable quirk to context bank 0.
> If context bank 0 is taken, move that context bank to another unused
> bank and rewrite the stream matching registers accordingly.

Is the only reason for dealing with the case that bank 0 is already in
use, due to the DMA domain that gets setup before driver probes?

I'm kinda thinking that we need to invent a way to unwind/detatch the
DMA domain, and unhook the iommu-dmaops, since this seems to already
be already causing problems with dma-bufs imported from other drivers
(who expect that dma_map_*(), with the importing device's dev ptr,
will do something sane.

BR,
-R

>
> This is be used by [1] and [2] to leave context bank 0 open so that
> the Adreno GPU can program it.
>
> [1] https://lists.linuxfoundation.org/pipermail/iommu/2020-January/041438.html
> [2] https://lists.linuxfoundation.org/pipermail/iommu/2020-January/041444.html
>
> Signed-off-by: Jordan Crouse <jcrouse@xxxxxxxxxxxxxx>
> ---
>
>  drivers/iommu/arm-smmu.c | 63 +++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 59 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 85a6773..799a254 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -254,6 +254,43 @@ static int __arm_smmu_alloc_bitmap(unsigned long *map, int start, int end)
>         return idx;
>  }
>
> +static void arm_smmu_write_s2cr(struct arm_smmu_device *smmu, int idx);
> +
> +static int __arm_smmu_alloc_cb(struct arm_smmu_device *smmu, int start,
> +               int target)
> +{
> +       int new, i;
> +
> +       /* Allocate a new context bank id */
> +       new = __arm_smmu_alloc_bitmap(smmu->context_map, start,
> +               smmu->num_context_banks);
> +
> +       if (new < 0)
> +               return new;
> +
> +       /* If no target is set or we actually got the bank index we wanted */
> +       if (target == -1 || new == target)
> +               return new;
> +
> +       /* Copy the context configuration to the new index */
> +       memcpy(&smmu->cbs[new], &smmu->cbs[target], sizeof(*smmu->cbs));
> +       smmu->cbs[new].cfg->cbndx = new;
> +
> +       /* FIXME: Do we need locking here? */
> +       for (i = 0; i < smmu->num_mapping_groups; i++) {
> +               if (smmu->s2crs[i].cbndx == target) {
> +                       smmu->s2crs[i].cbndx = new;
> +                       arm_smmu_write_s2cr(smmu, i);
> +               }
> +       }
> +
> +       /*
> +        * FIXME: Does getting here imply that 'target' is already set in the
> +        * context_map?
> +        */
> +       return target;
> +}
> +
>  static void __arm_smmu_free_bitmap(unsigned long *map, int idx)
>  {
>         clear_bit(idx, map);
> @@ -770,6 +807,7 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>         struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>         struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
>         unsigned long quirks = 0;
> +       int forcecb = -1;
>
>         mutex_lock(&smmu_domain->init_mutex);
>         if (smmu_domain->smmu)
> @@ -844,8 +882,25 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>                          * SEP_UPSTREAM so we don't need to reduce the size of
>                          * the ias to account for the sign extension bit
>                          */
> -                       if (smmu_domain->split_pagetables)
> -                               quirks |= IO_PGTABLE_QUIRK_ARM_TTBR1;
> +                       if (smmu_domain->split_pagetables) {
> +                               /*
> +                                * If split pagetables are enabled, assume that
> +                                * the user's intent is to use per-instance
> +                                * pagetables which, at least on a QCOM target,
> +                                * means that this domain should be on context
> +                                * bank 0.
> +                                */
> +
> +                               /*
> +                                * If we can't force to context bank 0 then
> +                                * don't bother enabling split pagetables which
> +                                * then would not allow aux domains
> +                                */
> +                               if (start == 0) {
> +                                       forcecb = 0;
> +                                       quirks |= IO_PGTABLE_QUIRK_ARM_TTBR1;
> +                               }
> +                       }
>                 } else if (cfg->fmt == ARM_SMMU_CTX_FMT_AARCH32_L) {
>                         fmt = ARM_32_LPAE_S1;
>                         ias = min(ias, 32UL);
> @@ -883,8 +938,8 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>                 ret = -EINVAL;
>                 goto out_unlock;
>         }
> -       ret = __arm_smmu_alloc_bitmap(smmu->context_map, start,
> -                                     smmu->num_context_banks);
> +
> +       ret = __arm_smmu_alloc_cb(smmu, start, forcecb);
>         if (ret < 0)
>                 goto out_unlock;
>
> --
> 2.7.4