Re: [PATCH V2] PCI/MSI: Set device flag indicating only 32-bit MSI support

[Vidya Sagar]

On 12/4/2020 1:24 AM, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
>
>
> On Fri, Dec 04, 2020 at 12:33:45AM +0530, Vidya Sagar wrote:
> > On 12/3/2020 11:54 PM, Bjorn Helgaas wrote:
> > > On Tue, Nov 24, 2020 at 04:20:35PM +0530, Vidya Sagar wrote:
> > > > There are devices (Ex:- Marvell SATA controller) that don't support
> > > > 64-bit MSIs and the same is advertised through their MSI capability
> > > > register. Set no_64bit_msi flag explicitly for such devices in the
> > > > MSI setup code so that the msi_verify_entries() API would catch
> > > > if the MSI arch code tries to use 64-bit MSI.
> > >
> > > This seems good to me.  I'll post a possible revision to set
> > > dev->no_64bit_msi in the device enumeration path instead of in the IRQ
> > > allocation path, since it's really a property of the device, not of
> > > the msi_desc.
> > >
> > > I like the extra checking this gives us.  Was this prompted by
> > > tripping over something, or is it something you noticed by code
> > > reading?  If the former, a hint about what was wrong and how it's
> > > being fixed would be useful.
> > I observed functionality issue with Marvell SATA controller (1b4b:9171) when
> > the allocated MSI target address was a 64-bit address. I mentioned the
> > Marvell SATA controller as an example in the commit message.
>
> I know you mentioned the Marvell controller, but apparently that
> device is working perfectly correctly: it does not support 64-bit MSI,
> and it does not advertise support for 64-bit MSI.
>
> So if there's a functionality issue, that means something is wrong in
> Linux that caused us to assign a 64-bit MSI address to it.  *That*
> issue is what I want to know about.  Your patch only warns about the
> issue; it doesn't fix it.
The issue is in the DWC code. I pushed a generic patch to fix that issue 
by specifying the limit of MSI target address to 32-bit region. Patch is 
up for review at 
http://patchwork.ozlabs.org/project/linux-pci/patch/20201117165312.25847-1-vidyas@xxxxxxxxxx/

> I don't think there's any point in specifically mentioning the Marvell
> device if it is working correctly, because the same issue should
> affect *any* device that doesn't support 64-bit MSI.  But if there's
> some arch code that incorrectly assigns a 64-bit address, it would
> definitely be useful to specify the arch.  And hopefully there's a fix
> for that arch code, too.
>
> > > > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
> > > > ---
> > > > V2:
> > > > * Addressed Bjorn's comment and changed the error message
> > > >
> > > >    drivers/pci/msi.c | 11 +++++++----
> > > >    1 file changed, 7 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> > > > index d52d118979a6..8de5ba6b4a59 100644
> > > > --- a/drivers/pci/msi.c
> > > > +++ b/drivers/pci/msi.c
> > > > @@ -581,10 +581,12 @@ msi_setup_entry(struct pci_dev *dev, int nvec, struct irq_affinity *affd)
> > > >         entry->msi_attrib.multi_cap     = (control & PCI_MSI_FLAGS_QMASK) >> 1;
> > > >         entry->msi_attrib.multiple      = ilog2(__roundup_pow_of_two(nvec));
> > > >
> > > > -     if (control & PCI_MSI_FLAGS_64BIT)
> > > > +     if (control & PCI_MSI_FLAGS_64BIT) {
> > > >                 entry->mask_pos = dev->msi_cap + PCI_MSI_MASK_64;
> > > > -     else
> > > > +     } else {
> > > >                 entry->mask_pos = dev->msi_cap + PCI_MSI_MASK_32;
> > > > +             dev->no_64bit_msi = 1;
> > > > +     }
> > > >
> > > >         /* Save the initial mask status */
> > > >         if (entry->msi_attrib.maskbit)
> > > > @@ -602,8 +604,9 @@ static int msi_verify_entries(struct pci_dev *dev)
> > > >         for_each_pci_msi_entry(entry, dev) {
> > > >                 if (!dev->no_64bit_msi || !entry->msg.address_hi)
> > > >                         continue;
> > > > -             pci_err(dev, "Device has broken 64-bit MSI but arch"
> > > > -                     " tried to assign one above 4G\n");
> > > > +             pci_err(dev, "Device has either broken 64-bit MSI or "
> > > > +                     "only 32-bit MSI support but "
> > > > +                     "arch tried to assign one above 4G\n");
> > > >                 return -EIO;
> > > >         }
> > > >         return 0;
> > > > --
> > > > 2.17.1