On Tue, Mar 24, 2020 at 06:00:31PM -0700, Kuppuswamy, Sathyanarayanan wrote: > Hi Bjorn, > > On 3/24/20 2:37 PM, Bjorn Helgaas wrote: > > This is really ugly. What's the story on this firmware? It sounds > > defective to me. > > I think there is no defined standard for this. I have checked few > _DSM implementations. Some of them return default value and some > don't. But atleast in the test hardware I use, we need this check. I agree that I don't see anything in the ACPI spec v6.3 about what should happen if we supply a Function Index that isn't supported. That looks like a hole in the spec. > > Or is everybody that uses _DSM supposed to check before evaluating it? > > I think its safer to do this check. > > > E.g., > > > > if (!acpi_check_dsm(...)) > > return -EINVAL; > > > > obj = acpi_evaluate_dsm(...); > > > > If everybody is supposed to do this, it seems like the check part > > should be moved into acpi_evaluate_dsm(). So my question, and I guess this is really for Rafael, is that since it seems like *everybody* needs to use acpi_check_dsm() in order to use acpi_evaluate_dsm() safely, why don't we move the check *into* acpi_evaluate_dsm()? It's just error prone if we expect everybody to call both interfaces. Bjorn
