[Xen-devel] [PATCH for 4.6 12/13] xen/iommu: smmu: Introduce automatic stream-id-masking

[Julien Grall <julien.grall@xxxxxxxxxx>]

From: Andreas Herrmann <andreas.herrmann@xxxxxxxxxxx>

Try to determine mask/id values that match several stream IDs of a
master device when doing Stream ID matching. Thus the number of used
SMR groups that are required to map all stream IDs of a master device
to a context should be less than the number of SMR groups used so far
(currently one SMR group is used for one stream ID).

Taken from the Linux ML:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-January/226100.html

Changes compare to the Linux ML version:
    - _fls doesn't exist on Xen so use fls
    - Use num_s2crs rather than num_streamids in the arm_smmu_free_smrs.
    This former is the field used to configure SRMS

Cc: Andreas Herrmann <herrmann.der.user@xxxxxxxxxxxxxx>
Signed-off-by: Andreas Herrmann <andreas.herrmann@xxxxxxxxxxx>
Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
---
 xen/drivers/passthrough/arm/smmu.c | 177 +++++++++++++++++++++++++++++++++----
 1 file changed, 162 insertions(+), 15 deletions(-)

diff --git a/xen/drivers/passthrough/arm/smmu.c 
b/xen/drivers/passthrough/arm/smmu.c
index bfc1069..8a6514f 100644
--- a/xen/drivers/passthrough/arm/smmu.c
+++ b/xen/drivers/passthrough/arm/smmu.c
@@ -43,6 +43,7 @@
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
+#include <linux/bitops.h>
 
 #include <linux/amba/bus.h>
 
@@ -346,8 +347,10 @@ struct arm_smmu_smr {
 };
 
 struct arm_smmu_master_cfg {
-       int                             num_streamids;
+       u32                             num_streamids;
        u16                             streamids[MAX_MASTER_STREAMIDS];
+       int                             num_s2crs;
+
        struct arm_smmu_smr             *smrs;
 };
 
@@ -392,6 +395,9 @@ struct arm_smmu_device {
        u32                             num_context_irqs;
        unsigned int                    *irqs;
 
+       u32                             smr_mask_mask;
+       u32                             smr_id_mask;
+
        struct list_head                list;
        struct rb_root                  masters;
 };
@@ -1113,6 +1119,137 @@ static void arm_smmu_free_pgtables(struct 
arm_smmu_domain *smmu_domain)
        kfree(pgd_base);
 }
 
+/*
+ * For a given set N of 2**order different stream IDs (no duplicates
+ * please!) we determine values mask and id such that
+ *
+ * (1)          (x & mask) == id
+ *
+ * for each stream ID x from the given set N.
+ *
+ * If the number of bits that are set in mask equals n, then there
+ * exist 2**n different values y for which
+ *
+ * (2)          (y & mask) == id
+ *
+ * Thus if n equals order we know that for the calculated mask and id
+ * values there are exactly 2**order == 2**n stream IDs for which (1)
+ * is true. And we finally can use mask and id to configure an SMR to
+ * match all stream IDs in the set N.
+ */
+static int determine_smr_mask(struct arm_smmu_device *smmu,
+                             struct arm_smmu_master_cfg *cfg,
+                             struct arm_smmu_smr *smr, int start, int order)
+{
+       u16 i, zero_bits_mask, one_bits_mask, const_mask;
+       int nr;
+
+       nr = 1 << order;
+
+       if (nr == 1) {
+               /* no mask, use streamid to match and be done with it */
+               smr->mask = 0;
+               smr->id = cfg->streamids[start];
+               return 0;
+       }
+
+       zero_bits_mask = 0;
+       one_bits_mask = 0xffff;
+       for (i = start; i < start + nr; i++) {
+               zero_bits_mask |= cfg->streamids[i];    /* const 0 bits */
+               one_bits_mask &= cfg->streamids[i];     /* const 1 bits */
+       }
+       zero_bits_mask = ~zero_bits_mask;
+
+       /* bits having constant values (either 0 or 1) */
+       const_mask = zero_bits_mask | one_bits_mask;
+
+       i = hweight16(~const_mask);
+       if (i == order) {
+               /*
+                * We have found a mask/id pair that matches exactly
+                * nr = 2**order stream IDs which we used for its
+                * calculation.
+                */
+               smr->mask = ~const_mask;
+               smr->id = one_bits_mask;
+       } else {
+               /*
+                * No usable mask/id pair for this set of streamids.
+                * If i > order then mask/id would match more than nr
+                * streamids.
+                * If i < order then mask/id would match less than nr
+                * streamids. (In this case we potentially have used
+                * some duplicate streamids for the calculation.)
+                */
+               return 1;
+       }
+
+       if (((smr->mask & smmu->smr_mask_mask) != smr->mask) ||
+               ((smr->id & smmu->smr_id_mask) != smr->id))
+               /* insufficient number of mask/id bits */
+               return 1;
+
+       return 0;
+}
+
+static int determine_smr_mapping(struct arm_smmu_device *smmu,
+                                struct arm_smmu_master_cfg *cfg,
+                                struct arm_smmu_smr *smrs, int max_smrs)
+{
+       int nr_sid, nr, i, bit, start;
+
+       /*
+        * This function is called only once -- when a master is added
+        * to a domain. If cfg->num_s2crs != 0 then this master
+        * was already added to a domain.
+        */
+       if (cfg->num_s2crs)
+               return -EINVAL;
+
+       start = nr = 0;
+       nr_sid = cfg->num_streamids;
+       do {
+               /*
+                * largest power-of-2 number of streamids for which to
+                * determine a usable mask/id pair for stream matching
+                */
+               bit = fls(nr_sid) - 1;
+               if (bit < 0)
+                       return 0;
+
+               /*
+                * iterate over power-of-2 numbers to determine
+                * largest possible mask/id pair for stream matching
+                * of next 2**i streamids
+                */
+               for (i = bit; i >= 0; i--) {
+                       if (!determine_smr_mask(smmu, cfg,
+                                               &smrs[cfg->num_s2crs],
+                                               start, i))
+                               break;
+               }
+
+               if (i < 0)
+                       goto out;
+
+               nr = 1 << i;
+               nr_sid -= nr;
+               start += nr;
+               cfg->num_s2crs++;
+       } while (cfg->num_s2crs <= max_smrs);
+
+out:
+       if (nr_sid) {
+               /* not enough mapping groups available */
+               cfg->num_s2crs = 0;
+               return -ENOSPC;
+       }
+
+       return 0;
+}
+
+
 static void arm_smmu_domain_destroy(struct iommu_domain *domain)
 {
        struct arm_smmu_domain *smmu_domain = domain->priv;
@@ -1129,7 +1266,7 @@ static void arm_smmu_domain_destroy(struct iommu_domain 
*domain)
 static int arm_smmu_master_configure_smrs(struct arm_smmu_device *smmu,
                                          struct arm_smmu_master_cfg *cfg)
 {
-       int i;
+       int i, max_smrs, ret;
        struct arm_smmu_smr *smrs;
        void __iomem *gr0_base = ARM_SMMU_GR0(smmu);
 
@@ -1139,31 +1276,32 @@ static int arm_smmu_master_configure_smrs(struct 
arm_smmu_device *smmu,
        if (cfg->smrs)
                return -EEXIST;
 
-       smrs = kmalloc_array(cfg->num_streamids, sizeof(*smrs), GFP_KERNEL);
+       max_smrs = min(smmu->num_mapping_groups, cfg->num_streamids);
+       smrs = kmalloc(sizeof(*smrs) * max_smrs, GFP_KERNEL);
        if (!smrs) {
                dev_err(smmu->dev, "failed to allocate %d SMRs\n",
-                       cfg->num_streamids);
+                       max_smrs);
                return -ENOMEM;
        }
 
+       ret = determine_smr_mapping(smmu, cfg, smrs, max_smrs);
+       if (ret)
+               goto err_free_smrs;
+
        /* Allocate the SMRs on the SMMU */
-       for (i = 0; i < cfg->num_streamids; ++i) {
+       for (i = 0; i < cfg->num_s2crs; ++i) {
                int idx = __arm_smmu_alloc_bitmap(smmu->smr_map, 0,
                                                  smmu->num_mapping_groups);
                if (IS_ERR_VALUE(idx)) {
                        dev_err(smmu->dev, "failed to allocate free SMR\n");
-                       goto err_free_smrs;
+                       goto err_free_bitmap;
                }
 
-               smrs[i] = (struct arm_smmu_smr) {
-                       .idx    = idx,
-                       .mask   = 0, /* We don't currently share SMRs */
-                       .id     = cfg->streamids[i],
-               };
+               smrs[i].idx = idx;
        }
 
        /* It worked! Now, poke the actual hardware */
-       for (i = 0; i < cfg->num_streamids; ++i) {
+       for (i = 0; i < cfg->num_s2crs; ++i) {
                u32 reg = SMR_VALID | smrs[i].id << SMR_ID_SHIFT |
                          smrs[i].mask << SMR_MASK_SHIFT;
                writel_relaxed(reg, gr0_base + ARM_SMMU_GR0_SMR(smrs[i].idx));
@@ -1172,9 +1310,11 @@ static int arm_smmu_master_configure_smrs(struct 
arm_smmu_device *smmu,
        cfg->smrs = smrs;
        return 0;
 
-err_free_smrs:
+err_free_bitmap:
        while (--i >= 0)
                __arm_smmu_free_bitmap(smmu->smr_map, smrs[i].idx);
+       cfg->num_s2crs = 0;
+err_free_smrs:
        kfree(smrs);
        return -ENOSPC;
 }
@@ -1190,13 +1330,15 @@ static void arm_smmu_master_free_smrs(struct 
arm_smmu_device *smmu,
                return;
 
        /* Invalidate the SMRs before freeing back to the allocator */
-       for (i = 0; i < cfg->num_streamids; ++i) {
+       for (i = 0; i < cfg->num_s2crs; ++i) {
                u8 idx = smrs[i].idx;
 
                writel_relaxed(~SMR_VALID, gr0_base + ARM_SMMU_GR0_SMR(idx));
                __arm_smmu_free_bitmap(smmu->smr_map, idx);
        }
 
+       cfg->num_s2crs = 0;
+
        cfg->smrs = NULL;
        kfree(smrs);
 }
@@ -1213,12 +1355,15 @@ static int arm_smmu_domain_add_master(struct 
arm_smmu_domain *smmu_domain,
        if (ret)
                return ret == -EEXIST ? 0 : ret;
 
-       for (i = 0; i < cfg->num_streamids; ++i) {
+       if (!cfg->num_s2crs)
+               cfg->num_s2crs = cfg->num_streamids;
+       for (i = 0; i < cfg->num_s2crs; ++i) {
                u32 idx, s2cr;
 
                idx = cfg->smrs ? cfg->smrs[i].idx : cfg->streamids[i];
                s2cr = S2CR_TYPE_TRANS |
                       (smmu_domain->cfg.cbndx << S2CR_CBNDX_SHIFT);
+               dev_dbg(smmu->dev, "S2CR%d: 0x%x\n", idx, s2cr);
                writel_relaxed(s2cr, gr0_base + ARM_SMMU_GR0_S2CR(idx));
        }
 
@@ -1890,6 +2035,8 @@ static int arm_smmu_device_cfg_probe(struct 
arm_smmu_device *smmu)
                                mask, sid);
                        return -ENODEV;
                }
+               smmu->smr_mask_mask = mask;
+               smmu->smr_id_mask = sid;
 
                dev_notice(smmu->dev,
                           "\tstream matching with %u register groups, mask 
0x%x",
-- 
2.1.3


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