From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6361AC2BBD0 for ; Tue, 8 Sep 2020 15:05:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 36BF123EB0 for ; Tue, 8 Sep 2020 15:05:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729037AbgIHPE5 (ORCPT ); Tue, 8 Sep 2020 11:04:57 -0400 Received: from netrider.rowland.org ([192.131.102.5]:38653 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1730125AbgIHPEU (ORCPT ); Tue, 8 Sep 2020 11:04:20 -0400 Received: (qmail 790483 invoked by uid 1000); 8 Sep 2020 10:32:03 -0400 Date: Tue, 8 Sep 2020 10:32:03 -0400 From: "stern@rowland.harvard.edu" To: Hamish Martin Cc: "linux-kernel@vger.kernel.org" , "gregkh@linuxfoundation.org" , "robh+dt@kernel.org" , "linux-usb@vger.kernel.org" , "devicetree@vger.kernel.org" Subject: Re: [PATCH 1/2] usb: ohci: Add per-port overcurrent quirk Message-ID: <20200908143203.GA789878@rowland.harvard.edu> References: <20200904032247.11345-1-hamish.martin@alliedtelesis.co.nz> <20200904032247.11345-2-hamish.martin@alliedtelesis.co.nz> <20200904154517.GB694058@rowland.harvard.edu> <9ba7b4dda9ef40e3c4c9b3f1c33075e04601ef61.camel@alliedtelesis.co.nz> <20200907145900.GC762136@rowland.harvard.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Mon, Sep 07, 2020 at 10:28:26PM +0000, Hamish Martin wrote: > On Mon, 2020-09-07 at 10:59 -0400, stern@rowland.harvard.edu wrote: > > On Mon, Sep 07, 2020 at 01:50:10AM +0000, Hamish Martin wrote: > > > Hi Alan, > > > > > > Thanks for your quick feedback. My replies are inline below. > > > > > > On Fri, 2020-09-04 at 11:45 -0400, Alan Stern wrote: > > > > On Fri, Sep 04, 2020 at 03:22:46PM +1200, Hamish Martin wrote: > > > > > Some integrated OHCI controller hubs do not expose all ports of > > > > > the > > > > > hub > > > > > to pins on the SoC. In some cases the unconnected ports > > > > > generate > > > > > spurious overcurrent events. For example the Broadcom > > > > > 56060/Ranger > > > > > 2 SoC > > > > > contains a nominally 3 port hub but only the first port is > > > > > wired. > > > > > > > > > > Default behaviour for ohci-platform driver is to use "ganged" > > > > > overcurrent protection mode. This leads to the spurious > > > > > overcurrent > > > > > events affecting all ports in the hub. > > > > > > > > > > Allow this to be rectified by specifying per-port overcurrent > > > > > protection > > > > > mode via the device tree. > > > > > > > > > > Signed-off-by: Hamish Martin > > > > > > > > > > --- > > > > > drivers/usb/host/ohci-hcd.c | 4 ++++ > > > > > drivers/usb/host/ohci-platform.c | 3 +++ > > > > > drivers/usb/host/ohci.h | 1 + > > > > > 3 files changed, 8 insertions(+) > > > > > > > > > > diff --git a/drivers/usb/host/ohci-hcd.c > > > > > b/drivers/usb/host/ohci- > > > > > hcd.c > > > > > index dd37e77dae00..01e3d75e29d9 100644 > > > > > --- a/drivers/usb/host/ohci-hcd.c > > > > > +++ b/drivers/usb/host/ohci-hcd.c > > > > > @@ -687,6 +687,10 @@ static int ohci_run (struct ohci_hcd > > > > > *ohci) > > > > > val |= RH_A_NPS; > > > > > ohci_writel (ohci, val, &ohci->regs- > > > > > >roothub.a); > > > > > } > > > > > + if (ohci->flags & OHCI_QUIRK_PER_PORT_OC) { > > > > > + val |= RH_A_OCPM; > > > > > + ohci_writel(ohci, val, &ohci->regs->roothub.a); > > > > > + } > > > > > > > > I don't think this is right, for two reasons. First, isn't per- > > > > port > > > > overcurrent protection the default? > > > > > > Not as far as I understand the current code. Just above where my > > > patch > > > applies, the RH_A_OCPM (and RH_A_PSM) bits are explicitly cleared > > > in > > > 'val' with: > > > val &= ~(RH_A_PSM | RH_A_OCPM); > > > > > > This, coupled with the OHCI_QUIRK_HUB_POWER being set by virtue of > > > the > > > 'distrust_firmware' module param defaulting true, reads to me like > > > the > > > default is for ganged over-current protection. And that is my > > > experience in this case. > > > > You're right about that. I hadn't noticed before; it makes little > > sense > > to have a quirk that defaults to true. > > > > It's not easy to tell the full story from the kernel history; that > > module parameter predates the Git era. I did learn that it was > > modified > > in 2.6.3-rc3 and goes back even farther: see > > > > https://marc.info/?l=linux-usb-devel&m=110628457424684&w=2 > > > > > If none of the quirks are selected then all of the fiddling with > > > 'val' > > > never gets written to 'ohci->regs->roothub.a' > > > > > > I'd appreciate your reading of that analysis because I'm by no > > > means > > > sure of it. > > > > > > > > > > > Second, RH_A_OCPM doesn't do anything unless RH_A_NOCP is clear. > > > > > > Correct, and that is my mistake. If I progress to a v2 of this > > > patch I > > > will update accordingly. > > > > Shall we try changing the parameter's default value? The USB > > subsystem > > is a lot more mature and reliable now than it was back in 2004. > > That doesn't really help me in my particular case. I tried turning the > param off and that just leads to the roothub.a reg not being modified > at all (and ganged over-current protection being left in place). > > So, I guess I'm still back to my original idea of adding a new quirk > (perhaps quirk is not the best name for it in this case) that allows > the per-port over-current to be selected. > If you would rather that this not be a quirk and I rework the code such > that if no other quirks are selected then we configure for per-port > over-current as the default then I can do that too. If you expect per- > port over-current to be the default then explicit code that enforces > that might be best. > > What's the best approach? In the absence of any evidence to the contrary, I think we should make per-port overcurrent handling be the default. So yes, add code which does that. Alan Stern