Re: [PATCH v2 1/8] iommu: Decouple iommu_present() from bus ops

[Jason Gunthorpe]

On Thu, Jan 26, 2023 at 06:26:16PM +0000, Robin Murphy wrote:
> Much as I'd like to remove iommu_present(), the final remaining users
> are proving stubbornly difficult to clean up, so kick that can down
> the road and just rework it to preserve the current behaviour without
> depending on bus ops.
> 
> Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> ---

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

This below might help. You might need to ask Thierry for help on the
problematic stuff in tegra. Really we should finish the series here
and organize things so that the domain allocation is defered until a
client is present.

https://lore.kernel.org/linux-iommu/20220106022053.2406748-1-baolu.lu@xxxxxxxxxxxxxxx/

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index cd5b18ef79512c..e5c257e41f4933 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
@@ -353,9 +353,6 @@ static int mtk_drm_kms_init(struct drm_device *drm)
 	if (drm_firmware_drivers_only())
 		return -ENODEV;
 
-	if (!iommu_present(&platform_bus_type))
-		return -EPROBE_DEFER;
-
 	pdev = of_find_device_by_node(private->mutex_node);
 	if (!pdev) {
 		dev_err(drm->dev, "Waiting for disp-mutex device %pOF\n",
@@ -709,6 +706,9 @@ static int mtk_drm_probe(struct platform_device *pdev)
 	int ret;
 	int i;
 
+	if (!device_iommu_mapped(dev))
+		return -EPROBE_DEFER;
+
 	private = devm_kzalloc(dev, sizeof(*private), GFP_KERNEL);
 	if (!private)
 		return -ENOMEM;