linux-kernel - Re: [PATCH v3 11/18] dmaengine: idxd: ims setup for the vdcm

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Date:   Fri, 9 Oct 2020 06:40:05 -0700
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        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,
        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,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v3 11/18] dmaengine: idxd: ims setup for the vdcm

On Fri, Oct 09, 2020 at 10:12:18AM -0300, Jason Gunthorpe wrote:
> On Fri, Oct 09, 2020 at 06:02:09AM -0700, Raj, Ashok wrote:
> > On Fri, Oct 09, 2020 at 09:49:45AM -0300, Jason Gunthorpe wrote:
> > > On Fri, Oct 09, 2020 at 05:43:07AM -0700, Raj, Ashok wrote:
> > > > On Fri, Oct 09, 2020 at 08:57:37AM -0300, Jason Gunthorpe wrote:
> > > > > On Thu, Oct 08, 2020 at 06:22:31PM -0700, Raj, Ashok wrote:
> > > > > 
> > > > > > Not randomly put there Jason :-).. There is a good reason for it. 
> > > > > 
> > > > > Sure the PASID value being associated with the IRQ make sense, but
> > > > > combining that register with the interrupt mask is just a compltely
> > > > > random thing to do.
> > > > 
> > > > Hummm... Not sure what you are complaining.. but in any case giving
> > > > hardware a more efficient way to store interrupt entries breaking any
> > > > boundaries that maybe implied by the spec is why IMS was defined.
> > > 
> > > I'm saying this PASID stuff is just some HW detail of IDXD and nothing
> > > that the core irqchip code should concern itself with
> > 
> > Ok, so you are saying this is device specific why is generic framework
> > having to worry about the PASID stuff? 
> > 
> > I thought we are consolidating code that otherwise similar drivers would
> > require anyway. I thought that's what Thomas was accomplishing with the new
> > framework.
> 
> My point is why would another driver combine PASID and the IRQ mask in
> one register? There is no spec saying to do this, no common design

IMS is a concept. How a device organizes its interrupt data is completely
hardware specific. Some vendor could keep them organized like how MSIx is
done today, and put PASID's in a separate offset. Or put all interrupt
related entries all in one place like how idxd handles it today.

Cheers,
Ashok