Re: [PATCH v1 1/3] iommu/riscv: Add iommu perf driver

From: Will Deacon <will@kernel.org>
To: 郭亚星 <guoyaxing@bosc.ac.cn>
Cc: linux-riscv <linux-riscv@lists.infradead.org>,
	iommu <iommu@lists.linux.dev>, tjeznach <tjeznach@rivosinc.com>,
	joro <joro@8bytes.org>, "robin.murphy" <robin.murphy@arm.com>,
	"paul.walmsley" <paul.walmsley@sifive.com>,
	palmer <palmer@dabbelt.com>, aou <aou@eecs.berkeley.edu>,
	alex <alex@ghiti.fr>, anxu <anxu@bosc.ac.cn>,
	wangran <wangran@bosc.ac.cn>
Subject: Re: [PATCH v1 1/3] iommu/riscv: Add iommu perf driver
Date: Thu, 18 Sep 2025 15:20:15 +0100	[thread overview]
Message-ID: <aMwVHrhKBZWstPat@willie-the-truck> (raw)
In-Reply-To: <48b8385a-ad44-4098-a647-109a3cfe3bbb@bosc.ac.cn>

On Thu, Sep 18, 2025 at 11:20:55AM +0800, 郭亚星 wrote:
> [Sorry, I tried switching a new email client and made some settings...]
> 
> On 9/17/2025 8:10 PM, Will Deacon wrote:
> > [nit: your email client has made a big mess of the thread here]
> > 
> > On Tue, Sep 16, 2025 at 06:27:23PM +0800, guoyaxing@bosc.ac.cn wrote:
> > > > PMU drivers are better placed under drivers/perf/
> > > 
> > > I did a quick reading of SMMU pmu driver in drivers/perf/.  However, If
> > > the RISC-V IOMMU PMU driver is placed under drivers/perf/ as the SMMU did,
> > > it would cause an overlap in the iomem resource region between the two
> > > devices(iommu & iommu pmu), because it needs to share interrupt-related
> > > registers (such as the IPSR register) with the main IOMMU driver.
> > 
> > Is that not something you can resolve with IRQF_SHARED?
> > 
> 
> Actually IOMMU perf is using stand-along interrupt, so might not need
> IRQF_SHARED with IOMMU driver.

Hrm. Two separate interrupts that share the same interrupt-handling
registers is an "interesting" design for a piece of hardware :/

> What I mean is the IOMMU and IOMMU perf share the same registers, such as
> IPSR. This could result in overlap on this iomem regions between them, which
> is highly undesirable.
> 
> For now, two ideas come to my mind:
> 1. Integrate IOMMU perf functionality into IOMMU driver, just as previous
> version patch.
> 
> 2. Let IOMMU driver export external api for IOMMU perf
> (to obtain virtual address of IPSR register) for perf related operations.
> 
> So what's your suggestion?

I wonder if you could create the PMU device as a child of the IOMMU?

I'm sure Robin had fun dealing with shared MMIO regions before, but I
can't remember the details (was it the CMN PMU driver?)

Will

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv