On Tue, Sep 03, 2013 at 10:18:24AM -0400, Tejun Heo wrote: > On Mon, Sep 02, 2013 at 11:00:28AM +0200, Alexander Gordeev wrote: > > + if (hpriv->flags & AHCI_HFLAG_NO_MSI) > > + goto intx; > > + > > + rc = pci_enable_msi_block_part(pdev, n_ports, AHCI_MAX_PORTS); We start with maximum possible number of ports AHCI_MAX_PORTS > > + if (!rc) > > + return AHCI_MAX_PORTS; If we succeeded the device is indeed supports all AHCI_MAX_PORTS and we report it. > > + if (rc < 0) > > + goto intx; If pci_enable_msi_block_part() failed we should not make further attempts and fallback to simple IRQ. > > + maxvec = rc; The device supports a lesser of AHCI_MAX_PORTS, because the previous pci_enable_msi_block_part() has not succeeded nor failed. Thus, rc contains number of supported MSIs. In case of ICH this will be 16 rather than 32. Actually, while I was writing this I realized this could be a number of MSIs that could have been enabled this device, not the maximum number of supported MSIs - these two may differ. I think MRSM should be checked. But I will continue as if it always the same. > > + rc = pci_enable_msi_block_part(pdev, n_ports, maxvec); Try pci_enable_msi_block_part() with the maximum number of supported MSIs. > > + if (!rc) > > + return maxvec; If we succeeded report the number of enabled MSIs. > > + if (rc < 0) > > + goto intx; If pci_enable_msi_block_part() failed we should not make further attempts and fallback to simple IRQ. > Why is the above fallback necessary? The only other number which > makes sense is roundup_pow_of_two(n_ports), right? What does the > above fallback logic buy us? We must enable maximum possible number of MSIs - the one reported in Multiple Message Capable register. Otherwise ICH device will fallback to MRSM. IOW, if the result of roundup_pow_of_two(n_ports) is not what in Multiple Message Capable register (i.e. as roundup_pow_of_two(6) vs 16) ICH will enforce MRSM mode. > Thanks. > > -- > tejun -- Regards, Alexander Gordeev agordeev@xxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
