[Xen-devel] Is msix_flush_writes() really needed? And multi_msi_*() flawed?

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

msix_flush_writes() is being called exclusively after calling 
msi_set_mask_bit(),
and that function already does follow writel() by readl() in the MSI-X case.

Also, isn't the single use of multi_msi_capable() broken (in the event that
the Multiple Message Capable field was 5, the shift would be undefined,
on x86 in particular would yield 1 as the result, where 0 would be needed),
and the subsequent twiddling of temp needlessly complicated (subtracting
one should be sufficient here).

And isn't multi_msi_enable(), though unused (since msi_{en,dis}able() are
unused), broken altogether (shifting num right by 1 instead of taking the
binary log)?

In case so:

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

---
 drivers/pci/msi.c |   30 ++----------------------------
 drivers/pci/msi.h |    2 +-
 2 files changed, 3 insertions(+), 29 deletions(-)

--- linux-2.6.28-rc3/drivers/pci/msi.c  2008-11-03 15:53:11.000000000 +0100
+++ 2.6.28-rc3-pci-msi-misc/drivers/pci/msi.c   2008-11-07 09:11:36.000000000 
+0100
@@ -103,29 +103,6 @@ static void msix_set_enable(struct pci_d
        }
 }
 
-static void msix_flush_writes(unsigned int irq)
-{
-       struct msi_desc *entry;
-
-       entry = get_irq_msi(irq);
-       BUG_ON(!entry || !entry->dev);
-       switch (entry->msi_attrib.type) {
-       case PCI_CAP_ID_MSI:
-               /* nothing to do */
-               break;
-       case PCI_CAP_ID_MSIX:
-       {
-               int offset = entry->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE +
-                       PCI_MSIX_ENTRY_VECTOR_CTRL_OFFSET;
-               readl(entry->mask_base + offset);
-               break;
-       }
-       default:
-               BUG();
-               break;
-       }
-}
-
 /*
  * PCI 2.3 does not specify mask bits for each MSI interrupt.  Attempting to
  * mask all MSI interrupts by clearing the MSI enable bit does not work
@@ -255,13 +232,11 @@ void write_msi_msg(unsigned int irq, str
 void mask_msi_irq(unsigned int irq)
 {
        msi_set_mask_bits(irq, 1, 1);
-       msix_flush_writes(irq);
 }
 
 void unmask_msi_irq(unsigned int irq)
 {
        msi_set_mask_bits(irq, 1, 0);
-       msix_flush_writes(irq);
 }
 
 static int msi_free_irqs(struct pci_dev* dev);
@@ -389,9 +364,8 @@ static int msi_capability_init(struct pc
                pci_read_config_dword(dev,
                        msi_mask_bits_reg(pos, entry->msi_attrib.is_64),
                        &maskbits);
-               temp = (1 << multi_msi_capable(control));
-               temp = ((temp - 1) & ~temp);
-               maskbits |= temp;
+               temp = 1U << (multi_msi_capable(control) - 1);
+               maskbits |= (temp << 1) - 1;
                pci_write_config_dword(dev, entry->msi_attrib.is_64, maskbits);
                entry->msi_attrib.maskbits_mask = temp;
        }
--- linux-2.6.28-rc3/drivers/pci/msi.h  2007-02-04 19:44:54.000000000 +0100
+++ 2.6.28-rc3-pci-msi-misc/drivers/pci/msi.h   2008-11-07 09:13:09.000000000 
+0100
@@ -23,7 +23,7 @@
 #define multi_msi_capable(control) \
        (1 << ((control & PCI_MSI_FLAGS_QMASK) >> 1))
 #define multi_msi_enable(control, num) \
-       control |= (((num >> 1) << 4) & PCI_MSI_FLAGS_QSIZE);
+       control |= ((ilog2(num) << 4) & PCI_MSI_FLAGS_QSIZE)
 #define is_64bit_address(control)      (!!(control & PCI_MSI_FLAGS_64BIT))
 #define is_mask_bit_support(control)   (!!(control & PCI_MSI_FLAGS_MASKBIT))
 #define msi_enable(control, num) multi_msi_enable(control, num); \




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