linux-kernel - Re: [PATCH v3 05/18] dmaengine: idxd: add IMS support in base driver

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Message-ID: <20200930185103.GT816047@nvidia.com>
Date:   Wed, 30 Sep 2020 15:51:03 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Dave Jiang <dave.jiang@...el.com>, <vkoul@...nel.org>,
        <megha.dey@...el.com>, <maz@...nel.org>, <bhelgaas@...gle.com>,
        <alex.williamson@...hat.com>, <jacob.jun.pan@...el.com>,
        <ashok.raj@...el.com>, <yi.l.liu@...el.com>, <baolu.lu@...el.com>,
        <kevin.tian@...el.com>, <sanjay.k.kumar@...el.com>,
        <tony.luck@...el.com>, <jing.lin@...el.com>,
        <dan.j.williams@...el.com>, <kwankhede@...dia.com>,
        <eric.auger@...hat.com>, <parav@...lanox.com>, <rafael@...nel.org>,
        <netanelg@...lanox.com>, <shahafs@...lanox.com>,
        <yan.y.zhao@...ux.intel.com>, <pbonzini@...hat.com>,
        <samuel.ortiz@...el.com>, <mona.hossain@...el.com>,
        <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <x86@...nel.org>, <linux-pci@...r.kernel.org>,
        <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 05/18] dmaengine: idxd: add IMS support in base driver

On Wed, Sep 30, 2020 at 08:47:00PM +0200, Thomas Gleixner wrote:

> > +	pci_read_config_dword(pdev, SIOVCAP(dvsec), &val32);
> > +	if ((val32 & 0x1) && idxd->hw.gen_cap.max_ims_mult) {
> > +		idxd->ims_size = idxd->hw.gen_cap.max_ims_mult * 256ULL;
> > +		dev_dbg(dev, "IMS size: %u\n", idxd->ims_size);
> > +		set_bit(IDXD_FLAG_SIOV_SUPPORTED, &idxd->flags);
> > +		dev_dbg(&pdev->dev, "IMS supported for device\n");
> > +		return;
> > +	}
> > +
> > +	dev_dbg(&pdev->dev, "SIOV unsupported for device\n");
> 
> It's really hard to find the code inside all of this dev_dbg()
> noise. But why is this capability check done in this driver? Is this
> capability stuff really IDXD specific or is the next device which
> supports this going to copy and pasta the above?

It is the weirdest thing, IMHO. Intel defined a dvsec cap in their
SIOV cookbook, but as far as I can see it serves no purpose at
all.

Last time I asked I got some unclear mumbling about "OEMs".

I expect you'll see all Intel drivers copying this code.

Jason