linux-kernel - Re: [patch V2 06/40] PCI/MSI: Provide static key for parent mask/unmask

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Date:   Thu, 24 Nov 2022 13:38:54 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, Will Deacon <will@...nel.org>,
        linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Andrew Lunn <andrew@...n.ch>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Ammar Faizi <ammarfaizi2@...weeb.org>,
        Robin Murphy <robin.murphy@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Nishanth Menon <nm@...com>, Tero Kristo <kristo@...nel.org>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Vinod Koul <vkoul@...nel.org>, Sinan Kaya <okaya@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>
Subject: Re: [patch V2 06/40] PCI/MSI: Provide static key for parent mask/unmask

On Thu, 24 Nov 2022 13:17:00 +0000,
Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> On Thu, Nov 24 2022 at 13:04, Marc Zyngier wrote:
> > On Mon, 21 Nov 2022 14:39:36 +0000,
> >>  static void pci_mask_msi(struct irq_data *data)
> >>  {
> >>  	struct msi_desc *desc = irq_data_get_msi_desc(data);
> >>  
> >>  	pci_msi_mask(desc, BIT(data->irq - desc->irq));
> >> +	cond_mask_parent(data);
> >
> > I find this a bit odd. If anything, I'd rather drop the masking at the
> > PCI level and keep it local to the interrupt controller, because this
> > is likely to be more universal than the equivalent PCI operation
> > (think multi-MSI, for example, which cannot masks individual MSIs).
> >
> > Another thing is that the static key is a global state. Nothing says
> > that masking one way or the other is a universal thing, specially when
> > you have multiple interrupt controllers dealing with MSIs in different
> > ways. For example, GICv3 can use both the ITS and the GICv3-MBI frame
> > at the same time for different PCI RC. OK, they happen to deal with
> > MSIs in the same way, but you hopefully get my point.
> 
> I'm fine with dropping that. I did this because basically all of the
> various ARM PCI/MSI domain implementation have a copy of the same
> functions. Some of them have pointlessly the wrong order because copy &
> pasta is so wonderful....
> 
> So the alternative solution is to provide _ONE_ set of correct callbacks
> and let the domain initialization code override the irq chip callbacks
> of the default PCI/MSI template.

If the various irqchips can tell the core code whether they want
things to be masked at the PCI level or at the irqchip level, this
would be a move in the right direction. For the GIC, I'd definitely
want things masked locally.

What I'd like to get rid off is the double masking, as I agree it is
on the "pretty dumb" side of things.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.