From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Subject: [v2] usb: usb251xb: Lock i2c-bus segment the hub resides From: Greg Kroah-Hartman Message-Id: <20190427104500.GA26765@kroah.com> Date: Sat, 27 Apr 2019 12:45:00 +0200 To: Serge Semin Cc: Richard Leitner , Serge Semin , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org List-ID: T24gU2F0LCBBcHIgMjcsIDIwMTkgYXQgMTI6MzE6MTFQTSArMDMwMCwgU2VyZ2UgU2VtaW4gd3Jv dGU6Cj4gT24gU2F0LCBBcHIgMjcsIDIwMTkgYXQgMDk6NTM6MjNBTSArMDIwMCwgR3JlZyBLcm9h aC1IYXJ0bWFuIHdyb3RlOgo+ID4gT24gU2F0LCBBcHIgMjcsIDIwMTkgYXQgMTA6Mzk6NDFBTSAr MDMwMCwgU2VyZ2UgU2VtaW4gd3JvdGU6Cj4gPiA+IE9uIFNhdCwgQXByIDI3LCAyMDE5IGF0IDA5 OjMyOjAwQU0gKzAyMDAsIEdyZWcgS3JvYWgtSGFydG1hbiB3cm90ZToKPiA+ID4gPiBPbiBTYXQs IEFwciAyNywgMjAxOSBhdCAxMDoxMDoyN0FNICswMzAwLCBTZXJnZSBTZW1pbiB3cm90ZToKPiA+ ID4gPiA+IE9uIFNhdCwgQXByIDI3LCAyMDE5IGF0IDA5OjAwOjQyQU0gKzAyMDAsIEdyZWcgS3Jv 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ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0E46B2087C; Sat, 27 Apr 2019 10:45:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556361903; bh=flwco3je1Q/uKS+Nq99CsLoSDI9a68ilfeV6XvEgXDY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ET+o2mRrk7w2HBVR1EVzWcjZyA8pi6hkypugsCtgm50yGKrmpeCCpZbWeXloZzieU RpG8ueOgAKOSY39GdswtldQ3NlpfZB4J4ezCYNe7iINVPoJE8ke73LCLvlEk/buc+A ecNL36YBKTPEUY+Fk2tFGgycvK4jMhsVogIlEUTc= Date: Sat, 27 Apr 2019 12:45:00 +0200 From: Greg Kroah-Hartman To: Serge Semin Cc: Richard Leitner , Serge Semin , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] usb: usb251xb: Lock i2c-bus segment the hub resides Message-ID: <20190427104500.GA26765@kroah.com> References: <20190424144914.10580-1-fancer.lancer@gmail.com> <20190426104650.30240-1-fancer.lancer@gmail.com> <20190427070042.GD28250@kroah.com> <20190427071025.hdrm3e5abnl4yock@mobilestation> <20190427073200.GB30973@kroah.com> <20190427073940.6yzhklfus4qd6ver@mobilestation> <20190427075323.GA31478@kroah.com> <20190427093110.3rx42ucv2zqjjnrp@mobilestation> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline In-Reply-To: <20190427093110.3rx42ucv2zqjjnrp@mobilestation> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Message-ID: <20190427104500.Gy-_QM1YT1qVY9QJ_Q4DTIumNZRV3wXCLNuPJv4LPRA@z> On Sat, Apr 27, 2019 at 12:31:11PM +0300, Serge Semin wrote: > On Sat, Apr 27, 2019 at 09:53:23AM +0200, Greg Kroah-Hartman wrote: > > On Sat, Apr 27, 2019 at 10:39:41AM +0300, Serge Semin wrote: > > > On Sat, Apr 27, 2019 at 09:32:00AM +0200, Greg Kroah-Hartman wrote: > > > > On Sat, Apr 27, 2019 at 10:10:27AM +0300, Serge Semin wrote: > > > > > On Sat, Apr 27, 2019 at 09:00:42AM +0200, Greg Kroah-Hartman wrote: > > > > > > On Fri, Apr 26, 2019 at 01:46:50PM +0300, Serge Semin wrote: > > > > > > > SMBus slave configuration is activated by CFG_SEL[1:0]=0x1 pins > > > > > > > state. This is the mode the hub is supposed to be to let this driver > > > > > > > work correctly. But a race condition might happen right after reset > > > > > > > is cleared due to CFG_SEL[0] pin being multiplexed with SMBus SCL > > > > > > > function. In case if the reset pin is handled by a i2c GPIO expander, > > > > > > > which is also placed at the same i2c-bus segment as the usb251x > > > > > > > SMB-interface connected to, then the hub reset clearance might > > > > > > > cause the CFG_SEL[0] being latched in unpredictable state. So > > > > > > > sometimes the hub configuration mode might be 0x1 (as expected), > > > > > > > but sometimes being 0x0, which doesn't imply to have the hub SMBus-slave > > > > > > > interface activated and consequently causes this driver failure. > > > > > > > > > > > > > > In order to fix the problem we must make sure the GPIO-reset chip doesn't > > > > > > > reside the same i2c-bus segment as the SMBus-interface of the hub. If > > > > > > > it doesn't, we can safely block the segment for the time the reset is > > > > > > > cleared to prevent anyone generating a traffic at the i2c-bus SCL lane > > > > > > > connected to the CFG_SEL[0] pin. But if it does, nothing we can do, so > > > > > > > just return an error. If we locked the i2c-bus segment and tried to > > > > > > > communicate with the GPIO-expander, it would cause a deadlock. If we didn't > > > > > > > lock the i2c-bus segment, it would randomly cause the CFG_SEL[0] bit flip. > > > > > > > > > > > > > > Signed-off-by: Serge Semin > > > > > > > Signed-off-by: Greg Kroah-Hartman > > > > > > > > > > > > I signed off on this? Where? When? > > > > > > > > > > > > never add a s-o-b line that you did not create, that implies a legal > > > > > > agreement. > > > > > > > > > > > > > > > > Ah, shit. Sorry. I should have added Acked-by. That's what I was going to do, > > > > > since you already added the first version of this into linux-next tree. But > > > > > apparently copy-pasted and left as is... > > > > > > > > If I have already applied a patch, I can't apply it again (or a > > > > different version.) You need to send a fix-up patch for the reported > > > > issue, not a whole new one as I can not go back in time and rewrite > > > > history. > > > > > > > > thanks, > > > > > > > > greg k-h > > > > > > Ok. Should I send it in reply to this patch or as a completely separate one? > > > > A separate one. > > Just did this. > > Two more questions. > > Is there any online service or ready-to-use configs-gen-script to build > patchsets locally with various kernel configs before sending them for review? > By using this I'd most likely prevent such unfortunate mistakes in future > patches. 'make allmodconfig' works for me. Also, the 0-day bot sometimes will test patches sent to the mailing list before they are applied, but that doesn't always work. > I suppose the situation like this isn't unique, and there are other patches > submitted with possible compilation problems. In this case seeing the linux-next > will be eventually integrated into the linux-stable, then at the point of those > patches the kernel source code will be build-broken corresponding config. > In this case wouldn't it be better to have some rebasable branch with build > robot service and fix the problematic patches in-place instead of > apply an incrementing commits? This also would keep the source code cleaner > at that particular commits. As this passed the first round of 0-day testing in my rebasable branch, I assumed it was good enough. But later testing found that not to be the case, which is pretty rare. And I can't have public trees that are rebasable as people work off of them, so we can just live with fixing this up. thanks, greg k-h