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: <20190427070042.GD28250@kroah.com> Date: Sat, 27 Apr 2019 09:00:42 +0200 To: Serge Semin Cc: Richard Leitner , Serge Semin , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org List-ID: T24gRnJpLCBBcHIgMjYsIDIwMTkgYXQgMDE6NDY6NTBQTSArMDMwMCwgU2VyZ2UgU2VtaW4gd3Jv dGU6Cj4gU01CdXMgc2xhdmUgY29uZmlndXJhdGlvbiBpcyBhY3RpdmF0ZWQgYnkgQ0ZHX1NFTFsx OjBdPTB4MSBwaW5zCj4gc3RhdGUuIFRoaXMgaXMgdGhlIG1vZGUgdGhlIGh1YiBpcyBzdXBwb3Nl ZCB0byBiZSB0byBsZXQgdGhpcyBkcml2ZXIKPiB3b3JrIGNvcnJlY3RseS4gQnV0IGEgcmFjZSBj b25kaXRpb24gbWlnaHQgaGFwcGVuIHJpZ2h0IGFmdGVyIHJlc2V0Cj4gaXMgY2xlYXJlZCBkdWUg dG8gQ0ZHX1NFTFswXSBwaW4gYmVpbmcgbXVsdGlwbGV4ZWQgd2l0aCBTTUJ1cyBTQ0wKPiBmdW5j dGlvbi4gSW4gY2FzZSBpZiB0aGUgcmVzZXQgcGluIGlzIGhhbmRsZWQgYnkgYSBpMmMgR1BJTyBl eHBhbmRlciwKPiB3aGljaCBpcyBhbHNvIHBsYWNlZCBhdCB0aGUgc2FtZSBpMmMtYnVzIHNlZ21l bnQgYXMgdGhlIHVzYjI1MXgKPiBTTUItaW50ZXJmYWNlIGNvbm5lY3RlZCB0bywgdGhlbiB0aGUg aHViIHJlc2V0IGNsZWFyYW5jZSBtaWdodAo+IGNhdXNlIHRoZSBDRkdfU0VMWzBdIGJlaW5nIGxh dGNoZWQgaW4gdW5wcmVkaWN0YWJsZSBzdGF0ZS4gU28KPiBzb21ldGltZXMgdGhlIGh1YiBjb25m aWd1cmF0aW9uIG1vZGUgbWlnaHQgYmUgMHgxIChhcyBleHBlY3RlZCksCj4gYnV0IHNvbWV0aW1l cyBiZWluZyAweDAsIHdoaWNoIGRvZXNuJ3QgaW1wbHkgdG8gaGF2ZSB0aGUgaHViIFNNQnVzLXNs YXZlCj4gaW50ZXJmYWNlIGFjdGl2YXRlZCBhbmQgY29uc2VxdWVudGx5IGNhdXNlcyB0aGlzIGRy aXZlciBmYWlsdXJlLgo+IAo+IEluIG9yZGVyIHRvIGZpeCB0aGUgcHJvYmxlbSB3ZSBtdXN0IG1h a2Ugc3VyZSB0aGUgR1BJTy1yZXNldCBjaGlwIGRvZXNuJ3QKPiByZXNpZGUgdGhlIHNhbWUgaTJj LWJ1cyBzZWdtZW50IGFzIHRoZSBTTUJ1cy1pbnRlcmZhY2Ugb2YgdGhlIGh1Yi4gSWYKPiBpdCBk b2Vzbid0LCB3ZSBjYW4gc2FmZWx5IGJsb2NrIHRoZSBzZWdtZW50IGZvciB0aGUgdGltZSB0aGUg cmVzZXQgaXMKPiBjbGVhcmVkIHRvIHByZXZlbnQgYW55b25lIGdlbmVyYXRpbmcgYSB0cmFmZmlj IGF0IHRoZSBpMmMtYnVzIFNDTCBsYW5lCj4gY29ubmVjdGVkIHRvIHRoZSBDRkdfU0VMWzBdIHBp bi4gQnV0IGlmIGl0IGRvZXMsIG5vdGhpbmcgd2UgY2FuIGRvLCBzbwo+IGp1c3QgcmV0dXJuIGFu IGVycm9yLiBJZiB3ZSBsb2NrZWQgdGhlIGkyYy1idXMgc2VnbWVudCBhbmQgdHJpZWQgdG8KPiBj b21tdW5pY2F0ZSB3aXRoIHRoZSBHUElPLWV4cGFuZGVyLCBpdCB3b3VsZCBjYXVzZSBhIGRlYWRs b2NrLiBJZiB3ZSBkaWRuJ3QKPiBsb2NrIHRoZSBpMmMtYnVzIHNlZ21lbnQsIGl0IHdvdWxkIHJh bmRvbWx5IGNhdXNlIHRoZSBDRkdfU0VMWzBdIGJpdCBmbGlwLgo+IAo+IFNpZ25lZC1vZmYtYnk6 IFNlcmdlIFNlbWluIDxmYW5jZXIubGFuY2VyQGdtYWlsLmNvbT4KPiBTaWduZWQtb2ZmLWJ5OiBH cmVnIEtyb2FoLUhhcnRtYW4gPGdyZWdraEBsaW51eGZvdW5kYXRpb24ub3JnPgoKSSBzaWduZWQg b2ZmIG9uIHRoaXM/ICBXaGVyZT8gIFdoZW4/CgpuZXZlciBhZGQgYSBzLW8tYiBsaW5lIHRoYXQg eW91IGRpZCBub3QgY3JlYXRlLCB0aGF0IGltcGxpZXMgYSBsZWdhbAphZ3JlZW1lbnQuCgpncmVn IGstaAo= 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=-5.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, T_DKIMWL_WL_HIGH,USER_AGENT_MUTT autolearn=unavailable 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 26C4BC43219 for ; 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Sat, 27 Apr 2019 07:00:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556348445; bh=vQajaea5nhD91IY5jg21FLw1xRj5+sMwfhWpfk73baQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KSoVVUT2szwR/MhdoPdWsJQwgPF1ycZ+gWjS+J4N+f6nVkM7fK3b/WNajFcguI7PG ScSXgj9zw8hWkKhGh2JVAEGLeyIqM0LnW4aWyvayu/nFP3Nnz9MFJFigVKhHrEcIkk rmzztQyEjsbx0w7ZyZJJiD7iUP14Zr/DqbB7nrhY= Date: Sat, 27 Apr 2019 09:00:42 +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: <20190427070042.GD28250@kroah.com> References: <20190424144914.10580-1-fancer.lancer@gmail.com> <20190426104650.30240-1-fancer.lancer@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline In-Reply-To: <20190426104650.30240-1-fancer.lancer@gmail.com> 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: <20190427070042.Hr7YRYldRGu8LVdZvrE8zrG60oUZGorGBrt6SCouw9s@z> 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. greg k-h