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=-5.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_MUTT 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 B1CBDC43218 for ; Sat, 27 Apr 2019 07:00:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E9FD2087C for ; Sat, 27 Apr 2019 07:00:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556348447; bh=vQajaea5nhD91IY5jg21FLw1xRj5+sMwfhWpfk73baQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ndMZL41Ios1SR2CnqMjl9CVfSdIw18J8tcKRtQKWWaUHlQiBpmcBiYyjeM+ew3t9Y B9G0fMQ7Wz43Fz5cwtBHGYD6Vo71ZGE1r4qszUVLix9LrUVpT0C7/yqXhDBk99VdXh uxEa2MrCPe2BVjf4EzTXcgKiN4aX/g/bwSlu8BKk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726358AbfD0HAq (ORCPT ); Sat, 27 Apr 2019 03:00:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:49196 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726001AbfD0HAq (ORCPT ); Sat, 27 Apr 2019 03:00:46 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AB4892077B; 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=us-ascii Content-Disposition: inline In-Reply-To: <20190426104650.30240-1-fancer.lancer@gmail.com> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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