Message-ID: <95eb8203-a332-37ae-28fb-5a2af4d1daba@intel.com>
Date:   Mon, 1 Jun 2020 15:09:45 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     vkoul@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, bhelgaas@...gle.com,
        gregkh@...uxfoundation.org, arnd@...db.de
Cc:     dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, dan.j.williams@...el.com, ashok.raj@...el.com,
        fenghua.yu@...el.com, tony.luck@...el.com, jing.lin@...el.com,
        sanjay.k.kumar@...el.com, dave.hansen@...el.com
Subject: Re: [PATCH v2 0/9] Add shared workqueue support for idxd driver

Vinod,
Obviously this series won't make it for 5.8 due to being blocked by Fenghua's 
PASID series. Do you think you can take patches 4 and 5 independently? I think 
these can go into 5.8 and is not dependent on anything. Thanks.

On 5/18/2020 11:53 AM, Dave Jiang wrote:
> v2:
> - Dropped device feature enabling (GregKH)
> - Dropped PCI device feature enabling (Bjorn)
> 	- https://members.pcisig.com/wg/PCI-SIG/document/14237
> 	- After some internal discussion, we have decided to hold off on the
> 	  enabling of DMWR due to the following reasons. 1. Most first gen hw
> 	  will not have the feature bits. 2. First gen hw that support the
> 	  feature are all Root Complex integrated endpoints. 3. PCI devices
> 	  that are not RCiEP’s with this capability won’t surface for a few
> 	  years so we can wait until we can test the full code.
> - Dropped special ioremap (hch)
> - Added proper support for WQ flush (tony, dan)
> - Changed descriptor submission to use sbitmap_queue for blocking. (dan)
> - Split out MOBDIR64B to right location for ENQCMDS placement. (daveh)
> - Split out SVM kernel dependencies for driver. (daveh)
> - Call enqcmds() directly (daveh)
> - Fix enqcmds() commit log (daveh)
> - Split out fault processing code (tony)
> 
> Driver stage 1 postings for context: [1]
> 
> The patch series has functionality dependency on Fenghua's "Tag application
> address space for devices" patch series for the ENQCMD CPU command enumeration
> and the PASID MSR support. [2]
> 
> The first patch enumerating ENQCMD is lifted from Fenghua's patch series. It
> removes the compilation dependency for the driver. It can be dropped by the
> maintainer merging the driver patch series once Fenghua's patch series is
> merged.
> 
> == Background ==
> A typical DMA device requires the driver to translate application buffers to
> hardware addresses, and a kernel-user transition to notify the hardware of new
> work. Shared Virtual Addressing (SVA) allows the processor and device to use the
> same virtual addresses without requiring software to translate between the
> address spaces. ENQCMD is a new instruction on Intel Platforms that allows user
> applications to directly notify hardware of new work, much like how doorbells
> are used in some hardware, but it carries a payload along with it. ENQCMDS is
> the supervisor version (ring0) of ENQCMD.
> 
> == ENQCMDS ==
> Introduce iosubmit_cmd512_sync(), a common wrapper that copies an input payload
> to a 64B aligned destination and confirms whether the payload was accepted by
> the device or not. iosubmit_cmd512_sync() wraps the new ENQCMDS CPU instruction.
> The ENQCMDS is a ring 0 CPU instruction that performs similar to the ENQCMD
> instruction. Descriptor submission must use ENQCMD(S) for shared workqueues
> (swq) on an Intel DSA device.
> 
> == Shared WQ support ==
> Introduce shared workqueue (swq) support for the idxd driver. The current idxd
> driver contains dedicated workqueue (dwq) support only. A dwq accepts
> descriptors from a MOVDIR64B instruction. MOVDIR64B is a posted instruction on
> the PCIe bus, it does not wait for any response from the device. If the wq is
> full, submitted descriptors are dropped. A swq utilizes the ENQCMDS in ring 0,
> which is a non-posted instruction. The zero flag would be set to 1 if the device
> rejects the descriptor or if the wq is full. A swq can be shared between
> multiple users (kernel or userspace) due to not having to keep track of the wq
> full condition for submission. A swq requires PASID and can only run with SVA
> support.
> 
> == IDXD SVA support ==
> Add utilization of PASID to support Shared Virtual Addressing (SVA). With PASID
> support, the descriptors can be programmed with host virtual address (HVA)
> rather than IOVA. The hardware will work with the IOMMU in fulfilling page
> requests. With SVA support, a user app using the char device interface can now
> submit descriptors without having to pin the virtual memory range it wants to
> DMA in its own address space.
> 
> The series does not add SVA support for the dmaengine subsystem. That support
> is coming at a later time.
> 
> [1]: https://lore.kernel.org/lkml/157965011794.73301.15960052071729101309.stgit@djiang5-desk3.ch.intel.com/
> [2]: https://lore.kernel.org/lkml/1585596788-193989-1-git-send-email-fenghua.yu@intel.com/
> [3]: https://software.intel.com/en-us/articles/intel-sdm
> [4]: https://software.intel.com/en-us/download/intel-scalable-io-virtualization-technical-specification
> [5]: https://software.intel.com/en-us/download/intel-data-streaming-accelerator-preliminary-architecture-specification
> [6]: https://01.org/blogs/2019/introducing-intel-data-streaming-accelerator
> [7]: https://intel.github.io/idxd/
> [8]: https://github.com/intel/idxd-driver idxd-stage2
> 
> ---
> 
> Dave Jiang (8):
>        x86/asm: move the raw asm in iosubmit_cmds512() to special_insns.h
>        x86/asm: add enqcmds() to support ENQCMDS instruction
>        dmaengine: idxd: add work queue drain support
>        dmaengine: idxd: move submission to sbitmap_queue
>        dmaengine: idxd: add shared workqueue support
>        dmaengine: idxd: clean up descriptors with fault error
>        dmaengine: idxd: add leading / for sysfspath in ABI documentation
>        dmaengine: idxd: add ABI documentation for shared wq
> 
> Fenghua Yu (1):
>        x86/cpufeatures: Enumerate ENQCMD and ENQCMDS instructions
> 
> 
>   Documentation/ABI/stable/sysfs-driver-dma-idxd |   68 ++++--
>   arch/x86/include/asm/cpufeatures.h             |    1
>   arch/x86/include/asm/io.h                      |   43 +++-
>   arch/x86/include/asm/special_insns.h           |   17 ++
>   arch/x86/kernel/cpu/cpuid-deps.c               |    1
>   drivers/dma/Kconfig                            |   15 +
>   drivers/dma/idxd/cdev.c                        |   38 ++++
>   drivers/dma/idxd/device.c                      |  252 +++++++++++++++---------
>   drivers/dma/idxd/dma.c                         |    9 -
>   drivers/dma/idxd/idxd.h                        |   32 ++-
>   drivers/dma/idxd/init.c                        |  122 +++++++-----
>   drivers/dma/idxd/irq.c                         |  184 ++++++++++++++----
>   drivers/dma/idxd/registers.h                   |   14 +
>   drivers/dma/idxd/submit.c                      |  105 ++++++----
>   drivers/dma/idxd/sysfs.c                       |  150 +++++++++++++-
>   15 files changed, 758 insertions(+), 293 deletions(-)
> 
> --
> 

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