linux-kernel - Re: [PATCH 5/6] x86/apic/msi: Use Real PCI DMA device when configuring IRTE

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Date:   Tue, 20 Oct 2020 21:21:31 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Derrick, Jonathan" <jonathan.derrick@...el.com>
Cc:     "hch@....de" <hch@....de>, "x86@...nel.org" <x86@...nel.org>,
        "Shevchenko, Andriy" <andriy.shevchenko@...el.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "andrzej.jakowski@...ux.intel.com" <andrzej.jakowski@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "Kalakota, SushmaX" <sushmax.kalakota@...el.com>
Subject: Re: [PATCH 5/6] x86/apic/msi: Use Real PCI DMA device when
 configuring IRTE

On Wed, Oct 21, 2020 at 01:20:24AM +0000, Derrick, Jonathan wrote:
> On Tue, 2020-10-20 at 15:26 -0500, Bjorn Helgaas wrote:
> > On Tue, Jul 28, 2020 at 01:49:44PM -0600, Jon Derrick wrote:
> > > VMD retransmits child device MSI/X with the VMD endpoint's requester-id.
> > > In order to support direct interrupt remapping of VMD child devices,
> > > ensure that the IRTE is programmed with the VMD endpoint's requester-id
> > > using pci_real_dma_dev().
> > > 
> > > Reviewed-by: Andy Shevchenko <andriy.shevchenko@...el.com>
> > > Signed-off-by: Jon Derrick <jonathan.derrick@...el.com>
> > 
> > As Thomas (and Stephen) pointed out, this conflicts with 7ca435cf857d
> > ("x86/irq: Cleanup the arch_*_msi_irqs() leftovers"), which removes
> > native_setup_msi_irqs().
> > 
> > Stephen resolved the conflict by dropping this hunk.  I would rather
> > just drop this patch completely from the PCI tree.  If I keep the
> > patch, (1) Linus will have to resolve the conflict, and worse, (2)
> > it's not clear what happened to the use of pci_real_dma_dev() here.
> > It will just vanish into the ether with no explanation other than
> > "this function was removed."
> > 
> > Is dropping this patch the correct thing to do?  Or do you need to add
> > pci_real_dma_dev() elsewhere to compensate?
>
> It would still need the pci_real_dma_dev() for IRTE programming.
> 
> I think at this point I would rather see 5+6 dropped and this included
> for TGL enablement:
> https://patchwork.kernel.org/project/linux-pci/patch/20200914190128.5114-1-jonathan.derrick@intel.com/

It's too late to add new things for v5.10.  I'll drop 5 and I'll be
happy to drop 6, too, if you want.  I have several comments/questions
on 6 anyway that I haven't finished writing up.

But if you'd rather have 1-4 + 6 in v5.10 instead of just 1-4, let me
know.

Bjorn