drm/nouveau/platform: probe IOMMU if present

Tegra SoCs have an IOMMU that can be used to present non-contiguous
physical memory as contiguous to the GPU and maximize the use of large
pages in the GPU MMU, leading to performance gains. This patch adds
support for probing such a IOMMU if present and make its properties
available in the nouveau_platform_gpu structure so subsystems can take
advantage of it.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

2 files changed, 92 insertions, 1 deletions

diff --git a/drivers/gpu/drm/nouveau/nouveau_platform.c b/drivers/gpu/drm/nouveau/nouveau_platform.c
index dc5900bf54ff..3691982452a9 100644
--- a/drivers/gpu/drm/nouveau/nouveau_platform.c
+++ b/drivers/gpu/drm/nouveau/nouveau_platform.c
@@ -27,6 +27,7 @@
 #include <linux/of.h>
 #include <linux/reset.h>
 #include <linux/regulator/consumer.h>
+#include <linux/iommu.h>
 #include <soc/tegra/fuse.h>
 #include <soc/tegra/pmc.h>
 
@@ -91,6 +92,71 @@ static int nouveau_platform_power_down(struct nouveau_platform_gpu *gpu)
         return 0;
 }
 
+static void nouveau_platform_probe_iommu(struct device *dev,
+                                         struct nouveau_platform_gpu *gpu)
+{
+        int err;
+        unsigned long pgsize_bitmap;
+
+        mutex_init(&gpu->iommu.mutex);
+
+        if (iommu_present(&platform_bus_type)) {
+                gpu->iommu.domain = iommu_domain_alloc(&platform_bus_type);
+                if (IS_ERR(gpu->iommu.domain))
+                        goto error;
+
+                /*
+                 * A IOMMU is only usable if it supports page sizes smaller
+                 * or equal to the system's PAGE_SIZE, with a preference if
+                 * both are equal.
+                 */
+                pgsize_bitmap = gpu->iommu.domain->ops->pgsize_bitmap;
+                if (pgsize_bitmap & PAGE_SIZE) {
+                        gpu->iommu.pgshift = PAGE_SHIFT;
+                } else {
+                        gpu->iommu.pgshift = fls(pgsize_bitmap & ~PAGE_MASK);
+                        if (gpu->iommu.pgshift == 0) {
+                                dev_warn(dev, "unsupported IOMMU page size\n");
+                                goto free_domain;
+                        }
+                        gpu->iommu.pgshift -= 1;
+                }
+
+                err = iommu_attach_device(gpu->iommu.domain, dev);
+                if (err)
+                        goto free_domain;
+
+                err = nvkm_mm_init(&gpu->iommu._mm, 0,
+                                   (1ULL << 40) >> gpu->iommu.pgshift, 1);
+                if (err)
+                        goto detach_device;
+
+                gpu->iommu.mm = &gpu->iommu._mm;
+        }
+
+        return;
+
+detach_device:
+        iommu_detach_device(gpu->iommu.domain, dev);
+
+free_domain:
+        iommu_domain_free(gpu->iommu.domain);
+
+error:
+        gpu->iommu.domain = NULL;
+        gpu->iommu.pgshift = 0;
+        dev_err(dev, "cannot initialize IOMMU MM\n");
+}
+
+static void nouveau_platform_remove_iommu(struct device *dev,
+                                          struct nouveau_platform_gpu *gpu)
+{
+        if (gpu->iommu.domain) {
+                iommu_detach_device(gpu->iommu.domain, dev);
+                iommu_domain_free(gpu->iommu.domain);
+        }
+}
+
 static int nouveau_platform_probe(struct platform_device *pdev)
 {
         struct nouveau_platform_gpu *gpu;
@@ -118,6 +184,8 @@ static int nouveau_platform_probe(struct platform_device *pdev)
         if (IS_ERR(gpu->clk_pwr))
                 return PTR_ERR(gpu->clk_pwr);
 
+        nouveau_platform_probe_iommu(&pdev->dev, gpu);
+
         err = nouveau_platform_power_up(gpu);
         if (err)
                 return err;
@@ -154,10 +222,15 @@ static int nouveau_platform_remove(struct platform_device *pdev)
         struct nouveau_drm *drm = nouveau_drm(drm_dev);
         struct nvkm_device *device = nvxx_device(&drm->device);
         struct nouveau_platform_gpu *gpu = nv_device_to_platform(device)->gpu;
+        int err;
 
         nouveau_drm_device_remove(drm_dev);
 
-        return nouveau_platform_power_down(gpu);
+        err = nouveau_platform_power_down(gpu);
+
+        nouveau_platform_remove_iommu(&pdev->dev, gpu);
+
+        return err;
 }
 
 #if IS_ENABLED(CONFIG_OF)
diff --git a/drivers/gpu/drm/nouveau/nouveau_platform.h b/drivers/gpu/drm/nouveau/nouveau_platform.h
index 268bb7213681..392874cf4725 100644
--- a/drivers/gpu/drm/nouveau/nouveau_platform.h
+++ b/drivers/gpu/drm/nouveau/nouveau_platform.h
@@ -24,10 +24,12 @@
 #define __NOUVEAU_PLATFORM_H__
 
 #include "core/device.h"
+#include "core/mm.h"
 
 struct reset_control;
 struct clk;
 struct regulator;
+struct iommu_domain;
 struct platform_driver;
 
 struct nouveau_platform_gpu {
@@ -36,6 +38,22 @@ struct nouveau_platform_gpu {
         struct clk *clk_pwr;
 
         struct regulator *vdd;
+
+        struct {
+                /*
+                 * Protects accesses to mm from subsystems
+                 */
+                struct mutex mutex;
+
+                struct nvkm_mm _mm;
+                /*
+                 * Just points to _mm. We need this to avoid embedding
+                 * struct nvkm_mm in os.h
+                 */
+                struct nvkm_mm *mm;
+                struct iommu_domain *domain;
+                unsigned long pgshift;
+        } iommu;
 };
 
 struct nouveau_platform_device {