From: Jisheng Zhang <jszhang@marvell.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
Joao Pinto <Joao.Pinto@synopsys.com>, Mason <slash.tmp@free.fr>,
Marc Zyngier <marc.zyngier@arm.com>,
linux-pci <linux-pci@vger.kernel.org>,
"Thibaud Cornic" <thibaud_cornic@sigmadesigns.com>,
LKML <linux-kernel@vger.kernel.org>,
Jingoo Han <jingoohan1@gmail.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
Subject: Re: [PATCH v9 2/3] PCI: Add tango PCIe host bridge support
Date: Tue, 4 Jul 2017 16:19:39 +0800 [thread overview]
Message-ID: <20170704161913.4935b16a@xhacker> (raw)
In-Reply-To: <CAKv+Gu9gi1W2Ex1hchMdob9PqkQ94uYspQW31W2+RG_sgsEV4Q@mail.gmail.com>
On Tue, 4 Jul 2017 09:02:06 +0100 Ard Biesheuvel wrote:
> On 4 July 2017 at 07:58, Jisheng Zhang <jszhang@marvell.com> 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@kernel.org> 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@sigmadesigns.com>
> >> > >> ---
> >> > >> 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.
> 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.
Thanks,
Jisheng
next prev parent reply other threads:[~2017-07-04 8:25 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-20 8:12 [PATCH v9 0/3] Tango PCIe controller support Marc Gonzalez
2017-06-20 8:14 ` [PATCH v9 1/3] PCI: Add DT binding for tango PCIe controller Marc Gonzalez
2017-06-20 8:17 ` [PATCH v9 2/3] PCI: Add tango PCIe host bridge support Marc Gonzalez
2017-07-02 23:18 ` Bjorn Helgaas
2017-07-03 9:35 ` Ard Biesheuvel
2017-07-03 13:27 ` Bjorn Helgaas
2017-07-04 6:58 ` Jisheng Zhang
2017-07-04 7:16 ` Jisheng Zhang
2017-07-04 8:02 ` Ard Biesheuvel
2017-07-04 8:19 ` Jisheng Zhang [this message]
2017-07-04 9:38 ` Ard Biesheuvel
2017-07-05 13:53 ` Joao Pinto
2017-07-03 9:54 ` Marc Gonzalez
2017-07-03 13:13 ` Marc Gonzalez
2017-07-03 15:30 ` Marc Gonzalez
2017-07-04 7:09 ` Peter Zijlstra
2017-07-04 13:08 ` Mason
2017-07-04 14:27 ` Peter Zijlstra
2017-07-04 15:18 ` Mason
2017-07-03 13:40 ` Bjorn Helgaas
2017-07-03 14:34 ` Marc Gonzalez
2017-07-04 15:58 ` Bjorn Helgaas
2017-07-04 23:42 ` Mason
2017-07-03 18:11 ` Russell King - ARM Linux
2017-07-03 18:44 ` Ard Biesheuvel
2017-07-04 15:15 ` Bjorn Helgaas
2017-07-04 18:17 ` Russell King - ARM Linux
2017-07-04 23:59 ` Mason
2017-07-05 5:21 ` Greg Kroah-Hartman
2017-07-05 12:33 ` Mark Brown
2017-06-20 8:18 ` [PATCH v9 3/3] PCI: Add tango MSI controller support Marc Gonzalez
2017-07-04 20:24 ` [PATCH v9 0/3] Tango PCIe " Bjorn Helgaas
2017-07-04 22:55 ` Mason
2017-07-05 18:03 ` Bjorn Helgaas
2017-07-05 20:39 ` Mason
2017-07-05 21:34 ` Bjorn Helgaas
2017-07-05 21:59 ` Mason
2017-07-06 3:39 ` Bjorn Helgaas
2017-07-06 12:26 ` Mason
2017-07-06 12:40 ` Marc Zyngier
2017-07-06 19:46 ` Bjorn Helgaas
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