Re: [PATCH v4 3/6] ACPI: Add driver for the VIOT table

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

On Thu, Jun 17, 2021 at 01:50:59PM +0200, Rafael J. Wysocki wrote:
> > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> > index be7da23fad76..b835ca702ff0 100644
> > --- a/drivers/acpi/bus.c
> > +++ b/drivers/acpi/bus.c
> > @@ -27,6 +27,7 @@
> >  #include <linux/dmi.h>
> >  #endif
> >  #include <linux/acpi_iort.h>
> > +#include <linux/acpi_viot.h>
> >  #include <linux/pci.h>
> >  #include <acpi/apei.h>
> >  #include <linux/suspend.h>
> > @@ -1339,6 +1340,7 @@ static int __init acpi_init(void)
> >         pci_mmcfg_late_init();
> >         acpi_iort_init();
> >         acpi_scan_init();
> > +       acpi_viot_init();
> 
> Is there a specific reason why to call it right here?
> 
> In particular, does it need to be called after acpi_scan_init()?  And
> does it need to be called before the subsequent functions?  If so,
> then why?

It does need to be called after acpi_scan_init(), because it relies on
struct device and their fwnode to be initialized. In particular to find a
PCI device we call pci_get_domain_bus_and_slot(), which needs the PCI
topology made available by acpi_scan_init().

It does not need to be before the subsequent functions however, I can move
it at the end.

> > +void __init acpi_viot_init(void)
> > +{
> > +       int i;
> > +       acpi_status status;
> > +       struct acpi_table_header *hdr;
> > +       struct acpi_viot_header *node;
> > +
> > +       status = acpi_get_table(ACPI_SIG_VIOT, 0, &hdr);
> > +       if (ACPI_FAILURE(status)) {
> > +               if (status != AE_NOT_FOUND) {
> > +                       const char *msg = acpi_format_exception(status);
> > +
> > +                       pr_err("Failed to get table, %s\n", msg);
> > +               }
> > +               return;
> > +       }
> > +
> > +       viot = (void *)hdr;
> > +
> > +       node = ACPI_ADD_PTR(struct acpi_viot_header, viot, viot->node_offset);
> > +       for (i = 0; i < viot->node_count; i++) {
> > +               if (viot_parse_node(node))
> > +                       return;
> > +
> > +               node = ACPI_ADD_PTR(struct acpi_viot_header, node,
> > +                                   node->length);
> > +       }
> 
> Do you still need the table after the above is complete?  If not,
> release the reference on it acquired above.

We don't need the table anymore, I'll drop the reference

Thanks,
Jean


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