Re: [Qemu-devel] [PATCH v3 6/6] spapr_pci: populate ibm,loc-code

[Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>]

David Gibson <david@gibson.dropbear.id.au> writes:

> On Wed, May 06, 2015 at 11:44:59AM +0530, Nikunj A Dadhania wrote:
>> Thomas Huth <thuth@redhat.com> writes:
>> 
>> > On Tue,  5 May 2015 14:23:56 +0530
>> > Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> wrote:
>> >
>> >> Each hardware instance has a platform unique location code.  The OF
>> >> device tree that describes a part of a hardware entity must include
>> >> the “ibm,loc-code” property with a value that represents the location
>> >> code for that hardware entity.
>> >> 
>> >> Populate ibm,loc-code.
>> >> 1) PCI passthru devices need to identify with its own ibm,loc-code
>> >>    available on the host.
>> >> 2) Emulated devices encode as following:
>> >>    qemu_<name>:<phb-index>:<slot>.<fn>
>> >> 
>> >> Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
>> >> ---
>> >>  hw/ppc/spapr_pci.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++-------
>> >>  1 file changed, 75 insertions(+), 11 deletions(-)
>> >> 
>> >> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
>> >> index cbd5661..eacf0bd 100644
>> >> --- a/hw/ppc/spapr_pci.c
>> >> +++ b/hw/ppc/spapr_pci.c
>> >> @@ -744,6 +744,70 @@ static AddressSpace *spapr_pci_dma_iommu(PCIBus *bus, void *opaque, int devfn)
>> >>      return &phb->iommu_as;
>> >>  }
>> >>  
>> >> +static bool spapr_phb_vfio_get_devspec_value(PCIDevice *pdev, char **value)
>> >> +{
>> >> +    char *host;
>> >> +    char path[PATH_MAX];
>> >> +
>> >> +    host = object_property_get_str(OBJECT(pdev), "host", NULL);
>> >> +    if (!host) {
>> >> +        return false;
>> >> +    }
>> >> +
>> >> +    snprintf(path, sizeof(path), "/sys/bus/pci/devices/%s/devspec", host);
>> >> +    g_free(host);
>> >> +
>> >> +    return g_file_get_contents(path, value, NULL, NULL);
>> >> +}
>> >> +
>> >> +static char *spapr_phb_vfio_get_loc_code(sPAPRPHBState *sphb,  PCIDevice *pdev)
>> >> +{
>> >> +    char path[PATH_MAX], *buf = NULL;
>> >> +
>> >> +    /* We have a vfio host bridge lets get the path. */
>> >> +    if (!spapr_phb_vfio_get_devspec_value(pdev, &buf)) {
>> >> +        return NULL;
>> >> +    }
>> >> +
>> >> +    snprintf(path, sizeof(path), "/proc/device-tree%s/ibm,loc-code", buf);
>> >> +    g_free(buf);
>> >> +
>> >> +    if (g_file_get_contents(path, &buf, NULL, NULL)) {
>> >> +        return buf;
>> >> +    } else {
>> >> +        return NULL;
>> >> +    }
>> >
>> > Minor idea for an optimization: g_file_get_contents() should set buf to
>> > NULL in case of errors anyway, so you could omit the "if" and
>> > "return NULLL" and simply always "return buf" here.
>> 
>> Sure
>> 
>> >
>> >> +}
>> >> +
>> >> +static char *spapr_phb_get_loc_code(sPAPRPHBState *sphb,  PCIDevice *pdev)
>> >> +{
>> >> +    char *path = g_malloc(PATH_MAX);
>> >> +
>> >> +    if (!path) {
>> >> +        return NULL;
>> >> +    }
>> >> +
>> >> +    /*
>> >> +     * For non-vfio devices and failures make up the location code out
>> >
>> > This comment ("and failures") ...
>> 
>> Oh right, one option is to drop that...
>> 
>> >
>> >> +     * of the name, slot and function.
>> >> +     *
>> >> +     *       qemu_<name>:<phb-index>:<slot>.<fn>
>> >> +     */
>> >> +    snprintf(path, PATH_MAX, "qemu_%s:%02d:%02d.%1d", pdev->name,
>> >> +             sphb->index, PCI_SLOT(pdev->devfn), PCI_FUNC(pdev->devfn));
>> >> +    return path;
>> >> +}
>> >> +
>> >> +
>> >> +static char *spapr_ibm_get_loc_code(sPAPRPHBState *sphb, PCIDevice *pdev)
>> >> +{
>> >> +    if (object_dynamic_cast(OBJECT(pdev), "vfio-pci") != NULL) {
>> >> +        return spapr_phb_vfio_get_loc_code(sphb, pdev);
>> >> +    } else {
>> >> +        return spapr_phb_get_loc_code(sphb, pdev);
>> >> +    }
>> >
>> > ... does not match quite the behavior here, as far as I can see. I
>> > guess you also wanted to fall back to spapr_phb_get_loc_code() in case 
>> > spapr_phb_vfio_get_loc_code() did not work as expected (eg. when the
>> > access to the /sys or /proc filesystem failed)?
>> 
>> ... In current case, if getting vfio device loc_code fails, we would not
>>  add any ibm,loc_code info. I thought that would be the proper
>>  behaviour. As "qemu_" would indicate it as an emulated device, which is
>>  not true. Or encode it as follows:
>> 
>> "vfio_<name>:<phb-index>:<slot>.<fn>"
>> 
>> So more checks would be needed here in that case:
>> 
>> if (vfio) {
>>    buf = vfio_get_loc_code()
>>    if (!buf) 
>>       buf = cook_vfio_get_loc_code()
>>    return buf;
>> } else { ... }
>
> If you can't determine the loc code, I think just leaving it out is
> probably the best option for now.  We can add fancier fallbacks in
> future if they seem like they make sense.

I already have the fancy version now, will send it for review.

Regards
Nikunj