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

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Date:	Wed, 13 Jul 2016 06:22:30 +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

> Subject: Re: PCIe MSI address is not written at pci_enable_msi_range call
>
> On 11/07/16 10:33, Bharat Kumar Gogada wrote:
> > 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.
>
> As a side question, how does setting the affinity work on this end-point if this
> involves changing the address programmed in the MSI registers?
> Do you expect the enabled bit to be toggled to around the write?
>

Yes,
Would anybody change MSI address in between wouldn't it cause race condition ?

Thanks & Regards,
Bharat


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