Re: [PATCH 0/3] PCI: designware: Fixing MSI handling flow

[Niklas Cassel <niklas.cassel@linaro.org>]

On Mon, Dec 03, 2018 at 10:42:19AM +0000, Lorenzo Pieralisi wrote:
> On Sun, Dec 02, 2018 at 12:50:58AM +0100, Niklas Cassel wrote:
> > On Wed, Nov 21, 2018 at 07:24:53PM +0200, Stanimir Varbanov wrote:
> > > Hi,
> > > 
> > > On 11/14/18 12:57 AM, Marc Zyngier wrote:
> > > > It recently came to light that the Designware PCIe driver is rather
> > > > broken in the way it handles MSI[1]:
> > > > 
> > > > - It masks interrupt by disabling them, meaning that MSIs generated
> > > >   during the masked window are simply lost. Oops.
> > > > 
> > > > - Acking of the currently pending MSI is done outside of the interrupt
> > > >   flow, getting moved around randomly and ultimately breaking the
> > > >   driver. Not great.
> > > > 
> > > > This series attempts to address this by switching to using the MASK
> > > > register for masking interrupts (!), and move the ack into the
> > > > appropriate callback, giving it a fixed place in the MSI handling
> > > > flow.
> > > > 
> > > > Note that this is only compile-tested on my arm64 laptop, as I'm
> > > > travelling and do not have the required HW to test it anyway. I'd
> > > > welcome both review and testing by the interested parties (dwc
> > > > maintainer and users affected by existing bugs).
> > > > 
> > > > Thanks,
> > > > 
> > > > 	M.
> > > > 
> > > > [1] https://patchwork.kernel.org/patch/10657987/
> > > > 
> > > > Marc Zyngier (3):
> > > >   PCI: designware: Use interrupt masking instead of disabling
> > > >   PCI: designware: Take lock when ACKing an interrupt
> > > >   PCI: designware: Move interrupt acking into the proper callback
> > > > 
> > > >  .../pci/controller/dwc/pcie-designware-host.c | 22 ++++++++++++-------
> > > >  1 file changed, 14 insertions(+), 8 deletions(-)
> > > > 
> > > 
> > > for pcie-qcom:
> > > 
> > > Tested-by: Stanimir Varbanov <svarbanov@mm-sol.com>
> > 
> > Hello PCI folks,
> > 
> > Since this is a real bug, we should try get a couple of Tested-by tags
> > before it's too late.
> > It would be nice if v4.20 was released without broken MSIs in this driver.
> > 
> > Personally I get confused just by looking at this mail thread.
> > 
> > I see 3 patches from Marc and a fix-up from Marc, but I also see
> > a patch from Gustavo, and another patch from Trent.
> > 
> > Is seems like Lorenzo has a branch with Marc's 3 patches + Marc's fix-up
> > folded in here:
> > https://git.kernel.org/pub/scm/linux/kernel/git/lpieralisi/pci.git/log/?h=test%2Fpci-dwc-msi
> > 
> > Perhaps it would be a good idea to send a V2, with proper Fixes-tags,
> > just so that people would know what to test, so that we can start getting
> > those Tested-by tags.
> 
> Perhaps it would be a good idea to pull the branch above and test it
> after I have sent three reminders to all DWC host bridge maintainers through
> this email thread.
> 
> I have no problem reposting those patches but it is time you started
> testing them, I have already explained what's the issue they are fixing
> in this thread, I do not think a Fixes: tag will add any further degree
> of urgency.
> 

I tested Lorenzo's
https://git.kernel.org/pub/scm/linux/kernel/git/lpieralisi/pci.git/log/?h=test%2Fpci-dwc-msi
branch with drivers/pci/controller/dwc/pcie-qcom.c.

Without this branch, when having an ath10k PCIe endpoint connected,
and simply running the ath10k as a host access point (running hostapd):
watch cat /proc/interrupts | grep ath10k_pci
I consistenly stop getting interrupts in less than a minute.

With this branch, I've been able to run the same test case successfully
for 30+ minutes.

Tested-by: Niklas Cassel <niklas.cassel@linaro.org>