Re: [PATCH v4] usb: xhci: allow imod-interval to be configurable

On Mon, Dec 04, 2017 at 09:27:51AM -0500, Adam Wallis wrote:

The xHCI driver currently has the IMOD set to 160, which
translates to an IMOD interval of 40,000ns (160 * 250)ns

Commit 0cbd4b34cda9 ("xhci: mediatek: support MTK xHCI host controller")
introduced a QUIRK for the MTK platform to adjust this interval to 20,
which translates to an IMOD interval of 5,000ns (20 * 250)ns. This is
due to the fact that the MTK controller IMOD interval is 8 times
as much as defined in xHCI spec.

Instead of adding more quirk bits for additional platforms, this patch
introduces the ability for vendors to set the IMOD_INTERVAL as is
optimal for their platform. By using device_property_read_u32() on
"imod-interval-ns", the IMOD INTERVAL can be specified in nano seconds.
If no interval is specified, the default of 40,000ns (IMOD=160) will be
used.

No bounds checking has been implemented due to the fact that a vendor
may have violated the spec and would need to specify a value outside of
the max 8,000 IRQs/second limit specified in the xHCI spec.

Tested-by: Chunfeng Yun <chunfeng.yun-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>
Signed-off-by: Adam Wallis <redacted>
---
changes from v3:
  * Changed imod-interval to imod-interval-ns [Rob Herring/Chunfeng]
  * Changed "modulation" to "moderation" throughout patch [Mathias]
changes from v2:
  * Added PCI default value [Mathias]
  * Removed xhci-mtk.h from xhci-plat.c [Chunfeng Yun]
  * Removed MTK quirk from xhci-plat and moved logic to xhci-mtk [Chunfeng]
  * Updated bindings Documentation to use proper units [Rob Herring]
  * Added imod-interval description and example to MTK binding documentation
changes from v1:
  * Removed device_property_read_u32() per suggestion from greg k-h
  * Used ER_IRQ_INTERVAL_MASK in place of (u16) cast

 Documentation/devicetree/bindings/usb/mediatek,mtk-xhci.txt | 2 ++
 Documentation/devicetree/bindings/usb/usb-xhci.txt          | 1 +
 drivers/usb/host/xhci-mtk.c                                 | 9 +++++++++
 drivers/usb/host/xhci-pci.c                                 | 3 +++
 drivers/usb/host/xhci-plat.c                                | 5 +++++
 drivers/usb/host/xhci.c                                     | 7 ++-----
 drivers/usb/host/xhci.h                                     | 2 ++
 7 files changed, 24 insertions(+), 5 deletions(-)

Reviewed-by: Rob Herring <redacted>

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