linux-kernel - RE: PCIe MSI address is not written at pci_enable_msi

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Date:	Mon, 11 Jul 2016 10:51:02 +0000
From:	Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
To:	Marc Zyngier <marc.zyngier@....com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	Arnd Bergmann <arnd@...db.de>, Bjorn Helgaas <bhelgaas@...gle.com>,
	nofooter <nofooter@...inx.com>
Subject: RE: PCIe MSI address is not written at pci_enable_msi_range call

> > Hi Marc,
> >
> > Thanks for the reply.
> >
> > From PCIe Spec:
> > MSI Enable Bit:
> > If 1 and the MSI-X Enable bit in the MSI-X Message
> > Control register (see Section 6.8.2.3) is 0, the
> > function is permitted to use MSI to request service
> > and is prohibited from using its INTx# pin.
> >
> > From Endpoint perspective, MSI Enable = 1 indicates MSI can be used
> which means MSI address and data fields are available/programmed.
> >
> > In our SoC whenever MSI Enable goes from 0 --> 1 the hardware latches
> onto MSI address and MSI data values.
> >
> > With current MSI implementation in kernel, our SoC is latching on to
> incorrect address and data values, as address/data
> > are updated much later than MSI Enable bit.
>
> Interesting. It looks like we're doing something wrong in the MSI flow.
> Can you confirm that this is limited to MSI and doesn't affect MSI-X?
>

I think it's the same issue irrespective of MSI or MSI-X as we are enabling these interrupts before providing
the  vectors.

So we always have a hole when MSI/MSI-X is 1, and software driver has not registered the irq, and End Point
may raise an interrupt (may be due to error) in this point of time.

Thanks & Regards,
Bharat

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