Date:   Thu, 17 Jun 2021 23:01:21 +0200
From:   Ferry Toth <fntoth@...il.com>
To:     Wesley Cheng <wcheng@...eaurora.org>, balbi@...nel.org,
        gregkh@...uxfoundation.org, robh+dt@...nel.org, agross@...nel.org,
        bjorn.andersson@...aro.org, frowand.list@...il.com
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        jackp@...eaurora.org, heikki.krogerus@...ux.intel.com,
        andy.shevchenko@...il.com
Subject: Re: [PATCH v10 0/6] Re-introduce TX FIFO resize for larger EP
 bursting

Hi

Op 17-06-2021 om 11:58 schreef Wesley Cheng:
> Changes in V10:
>   - Fixed compilation errors in config where OF is not used (error due to
>     unknown symbol for of_add_property()).  Add of_add_property() stub.
>   - Fixed compilation warning for incorrect argument being passed to dwc3_mdwidth
This fixes the OOPS I had in V9. I do not see any change in performance 
on Merrifield though.
> Changes in V9:
>   - Fixed incorrect patch in series.  Removed changes in DTSI, as dwc3-qcom will
>     add the property by default from the kernel.
>
> Changes in V8:
>   - Rebased to usb-testing
>   - Using devm_kzalloc for adding txfifo property in dwc3-qcom
>   - Removed DWC3 QCOM ACPI property for enabling the txfifo resize
>
> Changes in V7:
>   - Added a new property tx-fifo-max-num for limiting how much fifo space the
>     resizing logic can allocate for endpoints with large burst values.  This
>     can differ across platforms, and tie in closely with overall system latency.
>   - Added recommended checks for DWC32.
>   - Added changes to set the tx-fifo-resize property from dwc3-qcom by default
>     instead of modifying the current DTSI files.
>   - Added comments on all APIs/variables introduced.
>   - Updated the DWC3 YAML to include a better description of the tx-fifo-resize
>     property and added an entry for tx-fifo-max-num.
>
> Changes in V6:
>   - Rebased patches to usb-testing.
>   - Renamed to PATCH series instead of RFC.
>   - Checking for fs_descriptors instead of ss_descriptors for determining the
>     endpoint count for a particular configuration.
>   - Re-ordered patch series to fix patch dependencies.
>
> Changes in V5:
>   - Added check_config() logic, which is used to communicate the number of EPs
>     used in a particular configuration.  Based on this, the DWC3 gadget driver
>     has the ability to know the maximum number of eps utilized in all configs.
>     This helps reduce unnecessary allocation to unused eps, and will catch fifo
>     allocation issues at bind() time.
>   - Fixed variable declaration to single line per variable, and reverse xmas.
>   - Created a helper for fifo clearing, which is used by ep0.c
>
> Changes in V4:
>   - Removed struct dwc3* as an argument for dwc3_gadget_resize_tx_fifos()
>   - Removed WARN_ON(1) in case we run out of fifo space
>   
> Changes in V3:
>   - Removed "Reviewed-by" tags
>   - Renamed series back to RFC
>   - Modified logic to ensure that fifo_size is reset if we pass the minimum
>     threshold.  Tested with binding multiple FDs requesting 6 FIFOs.
>
> Changes in V2:
>   - Modified TXFIFO resizing logic to ensure that each EP is reserved a
>     FIFO.
>   - Removed dev_dbg() prints and fixed typos from patches
>   - Added some more description on the dt-bindings commit message
>
> Currently, there is no functionality to allow for resizing the TXFIFOs, and
> relying on the HW default setting for the TXFIFO depth.  In most cases, the
> HW default is probably sufficient, but for USB compositions that contain
> multiple functions that require EP bursting, the default settings
> might not be enough.  Also to note, the current SW will assign an EP to a
> function driver w/o checking to see if the TXFIFO size for that particular
> EP is large enough. (this is a problem if there are multiple HW defined
> values for the TXFIFO size)
>
> It is mentioned in the SNPS databook that a minimum of TX FIFO depth = 3
> is required for an EP that supports bursting.  Otherwise, there may be
> frequent occurences of bursts ending.  For high bandwidth functions,
> such as data tethering (protocols that support data aggregation), mass
> storage, and media transfer protocol (over FFS), the bMaxBurst value can be
> large, and a bigger TXFIFO depth may prove to be beneficial in terms of USB
> throughput. (which can be associated to system access latency, etc...)  It
> allows for a more consistent burst of traffic, w/o any interruptions, as
> data is readily available in the FIFO.
>
> With testing done using the mass storage function driver, the results show
> that with a larger TXFIFO depth, the bandwidth increased significantly.
>
> Test Parameters:
>   - Platform: Qualcomm SM8150
>   - bMaxBurst = 6
>   - USB req size = 256kB
>   - Num of USB reqs = 16
>   - USB Speed = Super-Speed
>   - Function Driver: Mass Storage (w/ ramdisk)
>   - Test Application: CrystalDiskMark
>
> Results:
>
> TXFIFO Depth = 3 max packets
>
> Test Case | Data Size | AVG tput (in MB/s)
> -------------------------------------------
> Sequential|1 GB x     |
> Read      |9 loops    | 193.60
> 	  |           | 195.86
>            |           | 184.77
>            |           | 193.60
> -------------------------------------------
>
> TXFIFO Depth = 6 max packets
>
> Test Case | Data Size | AVG tput (in MB/s)
> -------------------------------------------
> Sequential|1 GB x     |
> Read      |9 loops    | 287.35
> 	  |           | 304.94
>            |           | 289.64
>            |           | 293.61
> -------------------------------------------
>
> Wesley Cheng (6):
>    usb: gadget: udc: core: Introduce check_config to verify USB
>      configuration
>    usb: gadget: configfs: Check USB configuration before adding
>    usb: dwc3: Resize TX FIFOs to meet EP bursting requirements
>    of: Add stub for of_add_property()
>    usb: dwc3: dwc3-qcom: Enable tx-fifo-resize property by default
>    dt-bindings: usb: dwc3: Update dwc3 TX fifo properties
>
>   .../devicetree/bindings/usb/snps,dwc3.yaml         |  15 +-
>   drivers/usb/dwc3/core.c                            |   9 +
>   drivers/usb/dwc3/core.h                            |  15 ++
>   drivers/usb/dwc3/dwc3-qcom.c                       |   9 +
>   drivers/usb/dwc3/ep0.c                             |   2 +
>   drivers/usb/dwc3/gadget.c                          | 212 +++++++++++++++++++++
>   drivers/usb/gadget/configfs.c                      |  22 +++
>   drivers/usb/gadget/udc/core.c                      |  25 +++
>   include/linux/of.h                                 |   5 +
>   include/linux/usb/gadget.h                         |   5 +
>   10 files changed, 317 insertions(+), 2 deletions(-)
>

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