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SubjectRe: [RFC 02/13] driver core: Introduce MMIO configuration
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On 2021-02-26 14:02, Nicolas Saenz Julienne wrote:
> 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.

Devil's advocate: there already exist workarounds for 8-bit and/or
16-bit accesses not working in various places, does it make sense for a
64-bit workaround to be so wildly different and disjoint?

> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> ---
> 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

As mentioned previously, 32-bit systems may not need the overrides for
kernel I/O accessors, but they could still need the same workarounds for
the memory-mapping implications (if this is to be a proper generic
mechanism).

> + default n

Tip: it is always redundant to state that.

Robin.

> + 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;
>
>

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