linux-kernel - RE: [PATCHv5 04/20] PCI: mobiveil: Remove the flag MSI_FLAG_MULTI_PCI

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Date:   Mon, 1 Jul 2019 10:07:51 +0000
From:   "Z.q. Hou" <zhiqiang.hou@....com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "l.subrahmanya@...iveil.co.in" <l.subrahmanya@...iveil.co.in>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Leo Li <leoyang.li@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        Mingkai Hu <mingkai.hu@....com>,
        "M.h. Lian" <minghuan.lian@....com>,
        Xiaowei Bao <xiaowei.bao@....com>
Subject: RE: [PATCHv5 04/20] PCI: mobiveil: Remove the flag
 MSI_FLAG_MULTI_PCI_MSI

Hi Lorenzo,

Thanks a lot for your comments!

> -----Original Message-----
> From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Sent: 2019年6月28日 19:36
> To: Z.q. Hou <zhiqiang.hou@....com>
> Cc: linux-pci@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> devicetree@...r.kernel.org; linux-kernel@...r.kernel.org;
> bhelgaas@...gle.com; robh+dt@...nel.org; mark.rutland@....com;
> l.subrahmanya@...iveil.co.in; shawnguo@...nel.org; Leo Li
> <leoyang.li@....com>; catalin.marinas@....com; will.deacon@....com;
> Mingkai Hu <mingkai.hu@....com>; M.h. Lian <minghuan.lian@....com>;
> Xiaowei Bao <xiaowei.bao@....com>
> Subject: Re: [PATCHv5 04/20] PCI: mobiveil: Remove the flag
> MSI_FLAG_MULTI_PCI_MSI
> 
> On Mon, Jun 17, 2019 at 10:34:35AM +0000, Z.q. Hou wrote:
> 
> [...]
> 
> > > There is nothing obvious. Write what you are fixing in the commit
> > > log and I will apply the patch, I won't write the commit log for
> > > you. Anyone should be able to understand why a patch was needed by
> > > reading the commit log, it is as important as writing the code itself.
> >
> > With the flag MSI_FLAG_MULTI_PCI_MSI, when the Endpoint allocates
> > multiple MSI, it will trigger the "WARN_ON(nr_irqs != 1);" in
> > mobiveil_irq_msi_domain_alloc(), this is the issue this patch want to
> > fix.
> 
> And that's wrong. Marc explained why this controller does not support Multi
> MSI and that's what should go in the commit log, triggering a WARN_ON is
> the least of the problems (and the WARN_ON can even be removed after
> this patch is applied), if it was used as a bandaid to prevent allocating Multi
> MSI it is even more broken.
>

Yes, I agree, the root cause is hardware limitation, is the following changelog
acceptable?

Changelog:
The Mobiveil internal MSI controller uses separate target address per MSI,
so, it is unable to support Multiple MSI feature, which requires the same
target address and incremental MSI_DATA values. This patch is to remove
the flag MSI_FLAG_MULTI_PCI_MSI.

Thanks,
Zhiqiang
 
> Lorenzo
> 
> > Thanks,
> > Zhiqiang
> >
> > >
> > > Thanks,
> > > Lorenzo
> > >
> > > > Thanks,
> > > > Zhiqiang
> > > >
> > > > >
> > > > > Lorenzo
> > > > >
> > > > > > Subbu, did you test with Endpoint supporting multi MSI?
> > > > > >
> > > > > > Thanks,
> > > > > > Zhiqiang
> > > > > >
> > > > > > >
> > > > > > > Thanks,
> > > > > > > Lorenzo
> > > > > > >
> > > > > > > > Fixes: 1e913e58335f ("PCI: mobiveil: Add MSI support")
> > > > > > > > Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@....com>
> > > > > > > > Reviewed-by: Minghuan Lian <Minghuan.Lian@....com>
> > > > > > > > ---
> > > > > > > > V5:
> > > > > > > >  - Corrected the subject.
> > > > > > > >
> > > > > > > >  drivers/pci/controller/pcie-mobiveil.c | 2 +-
> > > > > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > > > >
> > > > > > > > diff --git a/drivers/pci/controller/pcie-mobiveil.c
> > > > > > > > b/drivers/pci/controller/pcie-mobiveil.c
> > > > > > > > index 563210e731d3..a0dd337c6214 100644
> > > > > > > > --- a/drivers/pci/controller/pcie-mobiveil.c
> > > > > > > > +++ b/drivers/pci/controller/pcie-mobiveil.c
> > > > > > > > @@ -703,7 +703,7 @@ static struct irq_chip
> > > > > > > > mobiveil_msi_irq_chip = {
> > > > > > > >
> > > > > > > >  static struct msi_domain_info mobiveil_msi_domain_info = {
> > > > > > > >  	.flags	= (MSI_FLAG_USE_DEF_DOM_OPS |
> > > > > > > MSI_FLAG_USE_DEF_CHIP_OPS |
> > > > > > > > -		   MSI_FLAG_MULTI_PCI_MSI | MSI_FLAG_PCI_MSIX),
> > > > > > > > +		   MSI_FLAG_PCI_MSIX),
> > > > > > > >  	.chip	= &mobiveil_msi_irq_chip,
> > > > > > > >  };
> > > > > > > >
> > > > > > > > --
> > > > > > > > 2.17.1
> > > > > > > >