On 3 July 2017 at 00:18, Bjorn Helgaas [off-list ref] wrote:

On Tue, Jun 20, 2017 at 10:17:40AM +0200, Marc Gonzalez wrote:

quoted

This driver is required to work around several hardware bugs
in the PCIe controller.

NB: Revision 1 does not support legacy interrupts, or IO space.

I had to apply these manually because of conflicts in Kconfig and
Makefile.  What are these based on?  Easiest for me is if you base
them on the current -rc1 tag.

quoted

Signed-off-by: Marc Gonzalez <redacted>
---
 drivers/pci/host/Kconfig      |   8 +++
 drivers/pci/host/Makefile     |   1 +
 drivers/pci/host/pcie-tango.c | 164 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/pci_ids.h       |   2 +
 4 files changed, 175 insertions(+)
 create mode 100644 drivers/pci/host/pcie-tango.c

[..]

quoted

+     /*
+      * QUIRK #2
+      * Unfortunately, config and mem spaces are muxed.
+      * Linux does not support such a setting, since drivers are free
+      * to access mem space directly, at any time.
+      * Therefore, we can only PRAY that config and mem space accesses
+      * NEVER occur concurrently.
+      */
+     writel_relaxed(1, pcie->mux);
+     ret = pci_generic_config_read(bus, devfn, where, size, val);
+     writel_relaxed(0, pcie->mux);

I'm very hesitant about this.  When people stress this, we're going to
get reports of data corruption.  Even with the disclaimer below, I
don't feel good about this.  Adding the driver is an implicit claim
that we support the device, but we know it can't be made reliable.

I noticed that the Synopsys driver suffers from a similar issue: in
dw_pcie_rd_other_conf(), it happily reprograms the outbound I/O window
to perform a config space access, and switches it back to I/O space
afterwards (unless it has more than 2 viewports, in which case it uses
dedicated windows for I/O space and config space)