[RFC 02/13] driver core: Introduce MMIO configuration

[Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>]

Some devices might inadvertently sit on buses that don't support 64bit
MMIO access, and need a mechanism to query these limitations without
prejudice to other buses in the system (i.e. defaulting to 32bit access
system wide isn't an option).

Introduce a new bus callback, 'mmio_configure(),' which will take care
of populating the relevant device properties based on the bus'
limitations.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
---
 arch/Kconfig               | 8 ++++++++
 drivers/base/dd.c          | 6 ++++++
 include/linux/device.h     | 3 +++
 include/linux/device/bus.h | 3 +++
 4 files changed, 20 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index 2bb30673d8e6..ba7f246b6b9d 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1191,6 +1191,14 @@ config ARCH_SPLIT_ARG64
 config ARCH_HAS_ELFCORE_COMPAT
 	bool
 
+config ARCH_HAS_64BIT_MMIO_BROKEN
+	bool
+	depends on 64BIT
+	default n
+	help
+	   Arch might contain busses unable to perform 64bit mmio accessses on
+	   an otherwise 64bit system.
+
 source "kernel/gcov/Kconfig"
 
 source "scripts/gcc-plugins/Kconfig"
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 9179825ff646..8086ce8f17a6 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -538,6 +538,12 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 			goto probe_failed;
 	}
 
+	if (dev->bus->mmio_configure) {
+		ret = dev->bus->mmio_configure(dev);
+		if (ret)
+			goto probe_failed;
+	}
+
 	if (driver_sysfs_add(dev)) {
 		pr_err("%s: driver_sysfs_add(%s) failed\n",
 		       __func__, dev_name(dev));
diff --git a/include/linux/device.h b/include/linux/device.h
index ba660731bd25..bd94aa0cbd72 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -553,6 +553,9 @@ struct device {
 #ifdef CONFIG_DMA_OPS_BYPASS
 	bool			dma_ops_bypass : 1;
 #endif
+#if defined(CONFIG_ARCH_HAS_64BIT_MMIO_BROKEN)
+	bool			mmio_64bit_broken:1;
+#endif
 };
 
 /**
diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
index 1ea5e1d1545b..680dfc3b4744 100644
--- a/include/linux/device/bus.h
+++ b/include/linux/device/bus.h
@@ -59,6 +59,8 @@ struct fwnode_handle;
  *		bus supports.
  * @dma_configure:	Called to setup DMA configuration on a device on
  *			this bus.
+ * @mmio_configure:	Called to setup MMIO configuration on a device on
+ *			this bus.
  * @pm:		Power management operations of this bus, callback the specific
  *		device driver's pm-ops.
  * @iommu_ops:  IOMMU specific operations for this bus, used to attach IOMMU
@@ -103,6 +105,7 @@ struct bus_type {
 	int (*num_vf)(struct device *dev);
 
 	int (*dma_configure)(struct device *dev);
+	int (*mmio_configure)(struct device *dev);
 
 	const struct dev_pm_ops *pm;
 
-- 
2.30.1