Re: designware/imx6: question regarding MSI

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

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.

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