linux-kernel - Re: [patch V2 43/46] genirq/msi: Provide and use msi_domain_set_default_info

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Date:   Fri, 28 Aug 2020 20:42:21 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Marc Zyngier <maz@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-hyperv@...r.kernel.org,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Jon Derrick <jonathan.derrick@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Wei Liu <wei.liu@...nel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Steve Wahl <steve.wahl@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Russ Anderson <rja@....com>, linux-pci@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        xen-devel@...ts.xenproject.org, Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Megha Dey <megha.dey@...el.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Baolu Lu <baolu.lu@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [patch V2 43/46] genirq/msi: Provide and use msi_domain_set_default_info_flags()

On Thu, Aug 27 2020 at 09:17, Marc Zyngier wrote:
> On 2020-08-26 12:17, Thomas Gleixner wrote:
>>  #ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
>> +void msi_domain_set_default_info_flags(struct msi_domain_info *info)
>> +{
>> +	/* Required so that a device latches a valid MSI message on startup 
>> */
>> +	info->flags |= MSI_FLAG_ACTIVATE_EARLY;
>
> As far as I remember the story behind this flag (it's been a while),
> it was working around a PCI-specific issue, hence being located in
> the PCI code.

Yes. Some cards misbehave when there is no valid message programmed and
MSI is enabled.

> Now, the "program the MSI before enabling it" concept makes sense no
> matter what bus this is on, and I wonder why we are even keeping this
> flag around.

> Can't we just drop it together with the check in
> msi_domain_alloc_irqs()?

I'm fine with that.

Thanks,

        tglx