linux-kernel - Re: [PATCH 0/3] usb: dwc3: ulpi: Fix UPLI registers read/write ops

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Message-ID: <87mu08c9qt.fsf@kernel.org>
Date:   Tue, 27 Oct 2020 11:13:14 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        David Cohen <david.a.cohen@...ux.intel.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] usb: dwc3: ulpi: Fix UPLI registers read/write ops

Serge Semin <Sergey.Semin@...kalelectronics.ru> writes:

> Our Baikal-T1 SoC is equipped with DWC USB3 IP core as a USB2.0 bus
> controller. In general the DWC USB3 driver is working well for it except
> the ULPI-bus part. We've found out that the DWC USB3 ULPI-bus driver detected
> PHY with VID:PID tuple as 0x0000:0x0000, which of course wasn't true since
> it was supposed to be 0x0424:0x0006. After a short digging inside the
> ulpi.c code and studying the DWC USB3 documentation, it has been
> discovered that the ULPI bus IO ops didn't work quite correct. The
> busy-loop had stopped waiting before the actual operation was finished. We
> found out that the problem was caused by several bugs hidden in the DWC
> USB3 ULPI-bus IO implementation.
>
> First of all in accordance with the DWC USB3 databook [1] the ULPI IO
> busy-loop is supposed to use the GUSB2PHYACCn.VStsDone flag as an
> indication of the PHY vendor control access completion. Instead it polled
> the GUSB2PHYACCn.VStsBsy flag, which as we discovered can be cleared a
> bit before the VStsDone flag.
>
> Secondly having the simple counter-based loop in the modern kernel is
> really a weak design of the busy-looping pattern especially seeing the
> ULPI operations delay can be easily estimated [2], since the bus clock is
> fixed to 60MHz.
>
> Finally the root cause of the denoted in the prologue problem was due to
> the Suspend PHY DWC USB3 feature perception. The commit e0082698b689
> ("usb: dwc3: ulpi: conditionally resume ULPI PHY") introduced the Suspend
> USB2.0 HS/FS/LS PHY regression as the Low-power consumption mode would be
> disable after a first attempt to read/write from the ULPI PHY control
> registers, and still didn't fix the problem it was originally intended for
> since the very first attempt of the ULPI PHY control registers IO would
> need much more time than the busy-loop provided. So instead of disabling
> the Suspend USB2.0 HS/FS/LS PHY feature we suggest to just extend the
> busy-loop delay in case if the GUSB2PHYCFGn.SusPHY flag set to 1. By doing
> so we'll eliminate the regression and the fix the false busy-loop timeout
> problem.
>
> [1] Synopsys DesignWare Cores SuperSpeed USB 3.0 xHCI Host Controller
>     Databook, 2.70a, December 2013, p.388
>
> [1] UTMI+ Low Pin Interface (ULPI) Specification, Revision 1.1,
>     October 20, 2004, pp. 30 - 36.
>
> Fixes: e0082698b689 ("usb: dwc3: ulpi: conditionally resume ULPI PHY")
> Fixes: 88bc9d194ff6 ("usb: dwc3: add ULPI interface support")
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> Cc: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
> Cc: Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>
> Cc: linux-usb@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org

these should go in the relevant commits instead.

> Serge Semin (3):
>   usb: dwc3: ulpi: Use VStsDone to detect PHY regs access completion
>   usb: dwc3: ulpi: Replace CPU-based busyloop with Protocol-based one
>   usb: dwc3: ulpi: Fix USB2.0 HS/FS/LS PHY suspend regression

make sure fixes don't depend on other rework otherwise they can't be
taken during the -rc cycle.

-- 
balbi

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