From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bin Liu Subject: Re: [PATCH] usb-musb: keep VBUS on when device is disconnected Date: Thu, 11 May 2017 14:10:05 -0500 Message-ID: <20170511191005.GG7154@uda0271908> References: <00882633-3F61-4010-A4D2-D04473282B10@tecnorama.it> <20170327131701.GA12674@uda0271908> <20170327143049.GG10760@atomide.com> <63FD9E13-2B70-485C-80A7-206BEC16905A@tecnorama.it> <20170327165946.GL10760@atomide.com> <20170327171534.GA4403@uda0271908> <20170327175536.GP10760@atomide.com> <20170511185038.GE7154@uda0271908> <20170511185528.GW3489@atomide.com> <20170511190100.GF7154@uda0271908> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <20170511190100.GF7154@uda0271908> Sender: linux-kernel-owner@vger.kernel.org To: Tony Lindgren , Moreno Bartalucci , Lars Melin , "linux-omap@vger.kernel.org" , "linux-usb@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Alessio Igor Bogani List-Id: linux-omap@vger.kernel.org On Thu, May 11, 2017 at 02:01:00PM -0500, Bin Liu wrote: > On Thu, May 11, 2017 at 11:55:28AM -0700, Tony Lindgren wrote: > > * Bin Liu [170511 11:53]: > > > On Mon, Mar 27, 2017 at 10:55:37AM -0700, Tony Lindgren wrote: > > > > * Bin Liu [170327 10:17]: > > > > > On Mon, Mar 27, 2017 at 09:59:47AM -0700, Tony Lindgren wrote: > > > > > > * Moreno Bartalucci [170327 09:23]: > > > > > > > If I understood your patch, however, if the device (anyone, not just my one) takes longer to switch, VBUS is deasserted anyway. > > > > > > > > > > > > Yeah some of them can take at least 10 seconds even to enumerate. > > > > > > So probably we need to have to have some longer timeout set for > > > > > > OTG_STATE_A_WAIT_BCON, like 20 or 30 seconds. > > > > > > > > > > > > > Although this patch is working for me, personally I would prefer a solution which would not deassert VBUS. At least on a host only port. Honestly I don’t know how a dual role port should work. > > > > > > > > > > > > It's been really long time since I read the OTG spec. There > > > > > > may be some diagram showing the required timeouts in the spec > > > > > > if there is one for VBUS. > > > > > > > > > > > > Maybe we need some property to specify vbus-always-on-in-host-mode? > > > > > > > > > > The MUSB otg state machine has been changed in many place since the last > > > > > time I looked at it, and I am not sure how exactly it works now. > > > > > > > > Yup.. I looked up the timers in the OTG spec and they are described > > > > in chapter "8.5.5.2" as a_wait_bcon_tmo or a_wait_bcon_tmr. But > > > > I could not find any values for them. > > > > > > > > Anyways, clearly we want things working with real devices :) > > > > > > > > > If the $subject patch can correctly keep the VBUS on for host-only mode, > > > > > we can somehow use dr_modei value to distinguish the mode. We don't have > > > > > to create a new vbus-always-on-in-host-mode flag. VBUS has to be always > > > > > on in host-only mode anyway, until some error condition happens. > > > > > > > > Yeh and it seems PM still works with the $subject patch also for > > > > host mode. So maybe that's enough to fix the issue. > > > > > > > > Also I don't have any idea why for ages we have been writing > > > > 0 to devctl there.. Maybe we've had a bug there that only now > > > > shows up when we idle things. > > > > > > The otg state machine implementation in the musb drivers are kind of strange. > > > OTG_STATE_A_WAIT_BCON suppose to be a steady state when no usb device is > > > attached, but the musb drivers use it as a transient state to handle error > > > cases, such as overcurrent ot HNP timeout, which is done in the 'case > > > OTG_STATE_A_WAIT_BCON' branch in otg_timer() (or dsps_check_status() for dsps > > > glue). > > > > > > Then later when 2f3fd2c5bde1 adds > > > > > > - /* Poll for ID change in OTG port mode */ > > > - if (musb->xceiv->otg->state == OTG_STATE_B_IDLE && > > > - musb->port_mode == MUSB_PORT_MODE_DUAL_ROLE) > > > + /* Poll for ID change and connect */ > > > + switch (musb->xceiv->otg->state) { > > > + case OTG_STATE_B_IDLE: > > > + case OTG_STATE_A_WAIT_BCON: > > > mod_timer(&glue->timer, jiffies + > > > msecs_to_jiffies(wrp->poll_timeout)); > > > + break; > > > > > > which causes dsps_check_status (or otg_timer()) got called for a normal > > > condition with OTG_STATE_A_WAIT_BCON, then turns off VBUS... > > > > > > Will try to see how to solve this... > > > > Maybe we just need to add back the earlier check for non-OTG devices > > "musb->port_mode == MUSB_PORT_MODE_DUAL_ROLE" into case > > OTG_STATE_A_WAIT_BCON? > > Not sure if it will work. The check is to kick out device-only mode. > DUAL_ROLE means both OTG and host-only. > > > > > Not sure if am335x configured with host port ever idle that way, > > but maybe VBUS can be kept on with musb idle. > > Just tried to remove > > + case OTG_STATE_A_WAIT_BCON: > > for the polling, but the port stops detecting device attach, musb > power/devctl registers are good, trying to see why... maybe related to > PM state? usb_otg_hs is idle, so not able to detect attach. So need to get the timer rolling in here to make it detect working. Maybe need to add a flag in dsps_check_status() to not turn off vbus in this case? Really don't like the idea... Regards, -Bin.