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

Hi Robin,

On Tue, 2021-03-02 at 11:29 +0000, Robin Murphy wrote:

On 2021-02-26 14:02, Nicolas Saenz Julienne wrote:

quoted

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?

Can you point out an example of the workarounds?

quoted

Signed-off-by: Nicolas Saenz Julienne <redacted>
---
  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).

I'll keep it in mind.

quoted

+	default n

Tip: it is always redundant to state that.

Noted!

Regards,
Nicolas