On 4 July 2017 at 09:19, Jisheng Zhang <jszhang@xxxxxxxxxxx> wrote: > On Tue, 4 Jul 2017 09:02:06 +0100 Ard Biesheuvel wrote: > >> On 4 July 2017 at 07:58, Jisheng Zhang <jszhang@xxxxxxxxxxx> wrote: >> > On Mon, 3 Jul 2017 08:27:04 -0500 wrote: >> > >> >> [+cc Jingoo, Joao] >> >> >> >> On Mon, Jul 03, 2017 at 10:35:50AM +0100, Ard Biesheuvel wrote: >> >> > On 3 July 2017 at 00:18, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: >> >> > > On Tue, Jun 20, 2017 at 10:17:40AM +0200, Marc Gonzalez wrote: >> >> > >> 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. >> >> > > >> >> > >> Signed-off-by: Marc Gonzalez <marc_gonzalez@xxxxxxxxxxxxxxxx> >> >> > >> --- >> >> > >> 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 >> >> > >> >> >> > [..] >> >> > >> + /* >> >> > >> + * 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) >> >> >> >> That doesn't sound good. Jingoo, Joao? I remember some discussion >> >> about this, but not the details. >> >> >> >> I/O accesses use wrappers (inb(), etc), so there's at least the >> >> possibility of a mutex to serialize them with respect to config >> >> accesses. >> >> >> > >> > IIRC, for 2 viewports, we don't need to worry about the config space >> > access, because config space access is serialized by pci_lock; We >> > do have race between config space and io space. But the accessing config >> > space and io space at the same time is rare. >> >> Being 'rare' is not sufficient, unfortunately. In the current >> situation, I/O space accesses may occur when the outbound window is >> directed to the config space of a potentially completely unrelated >> device. This is bad. > > Yep, I agree with you. > >> >> > And the PCIe EPs which >> > has io space are rare too, supporting these EPs are not the potential >> > target of those platforms with 2 viewports. >> > >> >> I am not sure EP mode is relevant here. What I do know is that boards > > I mean those PCIe EP cards which have IO space, but that doesn't matter. > Ah, ok. But if such EP cards are so rare, why expose I/O space at all if we cannot do it safely? >> like the Marvell 8040 based MacchiatoBin uses this IP in RC mode, and >> exposes config, MMIO and IO space windows using only 2 viewports. Note >> that this is essentially a bug in the DT description, given that its >> version of the IP supports 8 viewports. But the driver needs to be >> fixed as well. > > To fix for 2 viewports situation, we need to serialize access of the io > and config space. In internal repo, we can achieve it by modifying the > io access helper functions such as inl/outl, but this won't be accepted > by the mainline IMHO. Except fixing the HW, any elegant solution? > > Suggestions are appreciated. > I think the safe and upstreamable approach is to disable the I/O window completely if num-viewports <= 2.
