linux-kernel - RE: [PATCH 1/2] dmaengine: idxd: Expose DSA3.0 capabilities through sysfs

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Message-ID: <BL1SPRMB00111E4D037AA0922A61CA0C8877A@BL1SPRMB0011.namprd11.prod.outlook.com>
Date: Fri, 13 Jun 2025 22:26:23 +0000
From: "Lantz, Philip" <philip.lantz@...el.com>
To: Fenghua Yu <fenghuay@...dia.com>, "Sun, Yi" <yi.sun@...el.com>
CC: "Jin, Gordon" <gordon.jin@...el.com>, "Keshavamurthy, Anil S"
	<anil.s.keshavamurthy@...el.com>, "Jiang, Dave" <dave.jiang@...el.com>,
	"Gomes, Vinicius" <vinicius.gomes@...el.com>, "dmaengine@...r.kernel.org"
	<dmaengine@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] dmaengine: idxd: Expose DSA3.0 capabilities through
 sysfs



Fenghua wrote:

> Hi, Yi,
> 
> On 6/13/25 09:18, Yi Sun wrote:
> > Introduce sysfs interfaces for 3 new Data Streaming Accelerator (DSA)
> > capability registers (dsacap0-2) to enable userspace awareness of hardware
> > features in DSA version 3 and later devices.
> >
> > Userspace components (e.g. configure libraries, workload Apps) require this
> > information to:
> > 1. Select optimal data transfer strategies based on SGL capabilities
> > 2. Enable hardware-specific optimizations for floating-point operations
> > 3. Configure memory operations with proper numerical handling
> > 4. Verify compute operation compatibility before submitting jobs
> >
> > The output consists of values from the three dsacap registers, concatenated
> > in order and separated by commas.
> >
> > Example:
> > cat /sys/bus/dsa/devices/dsa0/dsacap
> >   0014000e000007aa,00fa01ff01ff03ff,000000000000f18d
> >
> > Signed-off-by: Yi Sun <yi.sun@...el.com>
> > Co-developed-by: Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
> > Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
> >
> > diff --git a/Documentation/ABI/stable/sysfs-driver-dma-idxd
> b/Documentation/ABI/stable/sysfs-driver-dma-idxd
> > index 4a355e6747ae..f9568ea52b2f 100644
> > --- a/Documentation/ABI/stable/sysfs-driver-dma-idxd
> > +++ b/Documentation/ABI/stable/sysfs-driver-dma-idxd
> > @@ -136,6 +136,21 @@ Description:	The last executed device administrative
> command's status/error.
> >   		Also last configuration error overloaded.
> >   		Writing to it will clear the status.
> >
> > +What:		/sys/bus/dsa/devices/dsa<m>/dsacap
> > +Date:		June 1, 2025
> > +KernelVersion:	6.17.0
> > +Contact:	dmaengine@...r.kernel.org
> > +Description:	The DSA3 specification introduces three new capability
> > +		registers: dsacap[0-2]. User components (e.g., configuration
> > +		libraries and workload applications) require this information
> > +		to properly utilize the DSA3 features.
> > +		This includes SGL capability support, Enabling hardware-specific
> > +		optimizations, Configuring memory, etc.
> > +		The output consists of values from the three dsacap registers,
> > +		concatenated in order and separated by commas.
> > +		This attribute should only be visible on DSA devices of version
> > +		3 or later.
> > +
> >   What:		/sys/bus/dsa/devices/dsa<m>/iaa_cap
> >   Date:		Sept 14, 2022
> >   KernelVersion: 6.0.0
> > diff --git a/drivers/dma/idxd/idxd.h b/drivers/dma/idxd/idxd.h
> > index 74e6695881e6..cc0a3fe1c957 100644
> > --- a/drivers/dma/idxd/idxd.h
> > +++ b/drivers/dma/idxd/idxd.h
> > @@ -252,6 +252,9 @@ struct idxd_hw {
> >   	struct opcap opcap;
> >   	u32 cmd_cap;
> >   	union iaa_cap_reg iaa_cap;
> > +	union dsacap0_reg dsacap0;
> > +	union dsacap1_reg dsacap1;
> > +	union dsacap2_reg dsacap2;
> >   };
> >
> >   enum idxd_device_state {
> > diff --git a/drivers/dma/idxd/init.c b/drivers/dma/idxd/init.c
> > index 80355d03004d..cc8203320d40 100644
> > --- a/drivers/dma/idxd/init.c
> > +++ b/drivers/dma/idxd/init.c
> > @@ -582,6 +582,10 @@ static void idxd_read_caps(struct idxd_device *idxd)
> >   	}
> >   	multi_u64_to_bmap(idxd->opcap_bmap, &idxd->hw.opcap.bits[0], 4);
> >
> > +	idxd->hw.dsacap0.bits = ioread64(idxd->reg_base +
> IDXD_DSACAP0_OFFSET);
> > +	idxd->hw.dsacap1.bits = ioread64(idxd->reg_base +
> IDXD_DSACAP1_OFFSET);
> > +	idxd->hw.dsacap2.bits = ioread64(idxd->reg_base +
> IDXD_DSACAP2_OFFSET);
> > +
> 
> The dsacaps are invalid for DSA 1 and 2. Not safe to read and assign the
> bits on DSA 1 and 2.
> 
> Better to assign the dsacap bits only when idxd.hw.version >= DSA_VERSION_3.

The registers are architecturally guaranteed to return 0 on prior versions, so it is
safe to read them on DSA 1 and 2 and there is no need for an additional check.

> [SNIP]