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PCI/MSI: Update MSI/MSI-X bits in PCIEBUS-HOWTO 

Update the MSI/MSI-X bits in PCIEBUS-HOWTO.  Stop talking about low-level
details that mention deprecated APIs and concentrate on what service
drivers should do and why.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
hifive-unleashed-5.1
Christoph Hellwig 2017-02-15 08:58:23 +01:00 committed by Bjorn Helgaas
parent c3cf2c61dd
commit e4e7d59704
1 changed files with 6 additions and 25 deletions
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31
Documentation/PCI/PCIEBUS-HOWTO.txt
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@ -161,21 +161,13 @@ Since all service drivers of a PCI-PCI Bridge Port device are
allowed to run simultaneously, below lists a few of possible resource
conflicts with proposed solutions.
6.1 MSI Vector Resource
6.1 MSI and MSI-X Vector Resource
The MSI capability structure enables a device software driver to call
pci_enable_msi to request MSI based interrupts. Once MSI interrupts
are enabled on a device, it stays in this mode until a device driver
calls pci_disable_msi to disable MSI interrupts and revert back to
INTx emulation mode. Since service drivers of the same PCI-PCI Bridge
port share the same physical device, if an individual service driver
calls pci_enable_msi/pci_disable_msi it may result unpredictable
behavior. For example, two service drivers run simultaneously on the
same physical Root Port. Both service drivers call pci_enable_msi to
request MSI based interrupts. A service driver may not know whether
any other service drivers have run on this Root Port. If either one
of them calls pci_disable_msi, it puts the other service driver
in a wrong interrupt mode.
Once MSI or MSI-X interrupts are enabled on a device, it stays in this
mode until they are disabled again. Since service drivers of the same
PCI-PCI Bridge port share the same physical device, if an individual
service driver enables or disables MSI/MSI-X mode it may result
unpredictable behavior.
To avoid this situation all service drivers are not permitted to
switch interrupt mode on its device. The PCI Express Port Bus driver
@ -187,17 +179,6 @@ driver. Service drivers should use (struct pcie_device*)dev->irq to
call request_irq/free_irq. In addition, the interrupt mode is stored
in the field interrupt_mode of struct pcie_device.
6.2 MSI-X Vector Resources
Similar to the MSI a device driver for an MSI-X capable device can
call pci_enable_msix to request MSI-X interrupts. All service drivers
are not permitted to switch interrupt mode on its device. The PCI
Express Port Bus driver is responsible for determining the interrupt
mode and this should be transparent to service drivers. Any attempt
by service driver to call pci_enable_msix/pci_disable_msix may
result unpredictable behavior. Service drivers should use
(struct pcie_device*)dev->irq and call request_irq/free_irq.
6.3 PCI Memory/IO Mapped Regions
Service drivers for PCI Express Power Management (PME), Advanced