Re: designware/imx6: question regarding MSI

[Pratyush Anand <pratyush.anand@st.com>]

On Thu, Jan 23, 2014 at 11:20:55PM +0800, Bjørn Erik Nilsen wrote:
> Hi Pratyush,
> 
> On Thu, 2014-01-23 at 07:51 +0100, Pratyush Anand wrote:
> > On Thu, Jan 23, 2014 at 01:52:19PM +0800, Jingoo Han wrote:
> > > On Thursday, January 23, 2014 5:39 AM, Jingoo Han wrote:
> > > > 
> > > > I’m currently playing with MSI support in pci-imx6.c using Harro Haan’s patch [*].
> > > > 
> > > > Are there any technical reasons why dw_pcie_msi_init cannot be called from dw_msi_setup_irq? Or rather,
> > > > why it should not?
> > > 
> > > No, there is no special reason.
> > > The patch (call dw_pcie_msi_init from dw_msi_setup_irq) would be
> > > good. Thank you for your effort.
> > > 
> > > Mohit, Pratyush,
> > > If you have different opinions, please let us know. :-)
> > 
> > dw_msi_setup_irq will be called for each function which needs msi
> > assignment. However, dw_pcie_msi_init should be called only once. So,
> > in my opinion calling dw_pcie_msi_init from dw_msi_setup_irq would not
> > be the best option.
> > 
> > @Bjørn, can you help us with tracing calling sequence of
> > dw_pcie_setup & dw_pcie_scan_bus. I think when you do "reset bridge",
> > it will call dw_pcie_setup and when you do "rescan bus", it will call
> > dw_pcie_scan_bus. If yes, then you can move dw_pcie_msi_init to
> > dw_pcie_setup.
> 
> 
> It looks like dw_pcie_setup and dw_pcie_scan_bus is only called when
> booting. Resetting the bridge or scanning the bus will not trigger any
> of these functions, unfortunately.

Yes, I browsed pcie sysfs rescan and reset code and it does not go
into that path. Sorry for the wrong pointers. I should have looked
into code earlier :(

Coming to the issue, I am still not convinced that msi_init part should
go to msi_setup_irq. May be something is missing.
@Mohit, Jingoo: How does remove, reset and rescan behave with your
platform.

Regards
Pratyush

> 
> I have looked for other hooks too, without luck.
> 
> > 
> > Regards
> > Pratyush
> > 
> > > 
> > > Best regards,
> > > Jingoo Han
> > > 
> > > > 
> > > > I’m asking because I have a hotplug scenario where this little hack (call dw_pcie_msi_init from
> > > > dw_msi_setup_irq) fixes a problem with MSI. I therefore need to understand whether it is a sensible
> > > > hack or just crap, and more importantly; how it can be fixed properly.
> > > > 
> > > > Scenario:
> > > > 
> > > > (remove endpoints)
> > > > # echo 1 > /sys/bus/pci/devices/0000:01:00.0/remove
> > > > # echo 1 > /sys/bus/pci/devices/0000:01:00.1/remove
> > > > 
> > > > # take fpga in and out of reset (this will mess up the configuration space of the bridge)
> > > > 
> > > > (reset bridge)
> > > > # echo 1 > /sys/bus/pci/devices/0000:00:00.0/reset
> > > > 
> > > > (rescan bus)
> > > > # echo 1 > /sys/bus/pci/rescan
> > > > 
> > > > At this point everything works fine except MSI. With above mention hack it works like a charm.
> > > > 
> > > > I would be grateful if someone could shed light on this. I might have missed some important details.
> > > > 
> > > > 
> > > > Best regards,
> > > > Bjørn Erik Nilsen
> > > > 
> > > > [*]
> > > > 
> > > > From: Harro Haan <hrhaan@gmail.com>
> > > > Date: Thu, 5 Dec 2013 14:06:37 +0100
> > > > Subject: [PATCH 2/2] PCI: imx6: add support for MSI
>