On Fri, Oct 11, 2024, at 11:12, Andy Shevchenko wrote:
> On Fri, Oct 11, 2024 at 09:59:46AM +0000, Arnd Bergmann wrote:
>> On Fri, Oct 11, 2024, at 09:53, Andy Shevchenko wrote:
>> > On Fri, Oct 11, 2024 at 06:18:18AM +0000, Arnd Bergmann wrote:
>> >> + if (!IS_ENABLED(CONFIG_HAS_IOPORT)) {
>> >> + *value = BIT_MASK(width);
>> >> + return AE_NOT_IMPLEMENTED;
>> >
>> > Perhaps it has already been discussed, but why do we need to file value with
>> > semi-garbage when we know it's invalid anyway?
>>
>> It's not strictly necessary, just precaution for possible callers
>> that use the resulting data without checking the error code.
>
> Do you have any examples of that in the kernel?
drivers/acpi/processor_throttling.c: acpi_os_read_port((acpi_io_address) throttling->status_register.
--
drivers/cpufreq/acpi-cpufreq.c-
drivers/cpufreq/acpi-cpufreq.c: acpi_os_read_port(reg->address, &val, reg->bit_width);
$ git grep ^[^=]*acpi_os_read_port
drivers/acpi/processor_throttling.c: acpi_os_read_port(\ (acpi_io_address) throttling->status_register.
drivers/cpufreq/acpi-cpufreq.c: acpi_os_read_port(reg->address, &val, reg->bit_width);
>> The all-ones data is what an x86 PC would see when an I/O
>> port is read that is not connected to any device.
>
> Yes, but it's not what your code does.
My bad, I was confused about what BIT_MASK() does.
I'll change it to "GENMASK(width, 0)", which should
do what I intended.
Arnd
