On Sun, Dec 14, 2014 at 02:45:36PM +0200, Laurent Pinchart wrote:
Hi Marek,
Thank you for the patch.
On Wednesday 19 November 2014 12:15:47 Marek Szyprowski wrote:
This patch introduces IOMMU_OF_DECLARE-based initialization to the driver, which replaces subsys_initcall-based procedure. exynos_iommu_of_setup ensures that each sysmmu controller is probed before its master device.
Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com
drivers/iommu/exynos-iommu.c | 28 +++++++++++++++++++++++++++- 1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/exynos-iommu.c b/drivers/iommu/exynos-iommu.c index cd28dc09db39..88f9afe641a0 100644 --- a/drivers/iommu/exynos-iommu.c +++ b/drivers/iommu/exynos-iommu.c
[snip]
@@ -1125,4 +1134,21 @@ err_reg_driver: kmem_cache_destroy(lv2table_kmem_cache); return ret; } -subsys_initcall(exynos_iommu_init);
+static int __init exynos_iommu_of_setup(struct device_node *np) +{
- struct platform_device *pdev;
- if (!init_done)
exynos_iommu_init();- pdev = of_platform_device_create(np, NULL, platform_bus_type.dev_root);
- if (IS_ERR(pdev))
return PTR_ERR(pdev);If we end up having to create the IOMMU platform devices from within the drivers, the introduction of IOMMU_OF_DECLARE starts to feel like a workaround to me. I wonder whether it wouldn't then be better to let the driver core instantiate the IOMMU platform device from DT as for all other devices, and use device notifiers to defer probe of the bus masters until the required IOMMU(s) are registered.
Notifiers don't work very well for this. Notifier blocks are supposed to return a very limited number of values, so sneaking in a -EPROBE_DEFER isn't likely to work out very well.
This was in fact one of Hiroshi's proposals over a year ago and got refused because of those reasons. The next solution was to introduce a function, not very much unlike the of_iommu_configure() that would be called in the core prior to calling into the driver's ->probe() callback so that it could handle this at probe time (as opposed to device creation time). That way the core can easily defer probe if the IOMMU is not there yet. At the same time it can simply use the driver model without requiring per-architecture hacks or workarounds.
Note that there is really no need for any of this configuration or initialization to happen at device creation time. Drivers won't be able to use the IOMMU or DMA APIs until their .probe(), so handling this any earlier is completely unnecessary.
Thierry