}
}
+static bool host1x_wants_iommu(struct host1x *host1x)
+{
+ /*
+ * If we support addressing a maximum of 32 bits of physical memory
+ * and if the host1x firewall is enabled, there's no need to enable
+ * IOMMU support. This can happen for example on Tegra20, Tegra30
+ * and Tegra114.
+ *
+ * Tegra124 and later can address up to 34 bits of physical memory and
+ * many platforms come equipped with more than 2 GiB of system memory,
+ * which requires crossing the 4 GiB boundary. But there's a catch: on
+ * SoCs before Tegra186 (i.e. Tegra124 and Tegra210), the host1x can
+ * only address up to 32 bits of memory in GATHER opcodes, which means
+ * that command buffers need to either be in the first 2 GiB of system
+ * memory (which could quickly lead to memory exhaustion), or command
+ * buffers need to be treated differently from other buffers (which is
+ * not possible with the current ABI).
+ *
+ * A third option is to use the IOMMU in these cases to make sure all
+ * buffers will be mapped into a 32-bit IOVA space that host1x can
+ * address. This allows all of the system memory to be used and works
+ * within the limitations of the host1x on these SoCs.
+ *
+ * In summary, default to enable IOMMU on Tegra124 and later. For any
+ * of the earlier SoCs, only use the IOMMU for additional safety when
+ * the host1x firewall is disabled.
+ */
+ if (host1x->info->dma_mask <= DMA_BIT_MASK(32)) {
+ if (IS_ENABLED(CONFIG_TEGRA_HOST1X_FIREWALL))
+ return false;
+ }
+
+ return true;
+}
+
static struct iommu_domain *host1x_iommu_attach(struct host1x *host)
{
struct iommu_domain *domain = iommu_get_domain_for_dev(host->dev);
int err;
/*
- * If the host1x firewall is enabled, there's no need to enable IOMMU
- * support. Similarly, if host1x is already attached to an IOMMU (via
- * the DMA API), don't try to attach again.
+ * We may not always want to enable IOMMU support (for example if the
+ * host1x firewall is already enabled and we don't support addressing
+ * more than 32 bits of physical memory), so check for that first.
+ *
+ * Similarly, if host1x is already attached to an IOMMU (via the DMA
+ * API), don't try to attach again.
*/
- if (IS_ENABLED(CONFIG_TEGRA_HOST1X_FIREWALL) || domain)
+ if (!host1x_wants_iommu(host) || domain)
return domain;
host->group = iommu_group_get(host->dev);