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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2DB6FC433FE for ; Wed, 18 May 2022 15:52:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239744AbiERPwR (ORCPT ); Wed, 18 May 2022 11:52:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47896 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239593AbiERPwP (ORCPT ); Wed, 18 May 2022 11:52:15 -0400 Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16A4F1C83EB; Wed, 18 May 2022 08:52:14 -0700 (PDT) Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.17.1.5/8.17.1.5) with ESMTP id 24IFElLE013025; Wed, 18 May 2022 15:51:29 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=message-id : date : mime-version : subject : from : to : cc : references : in-reply-to : content-type : content-transfer-encoding; s=pp1; bh=AM2xQGtGTyOcD/kklWCco7altrVDggH1p+vQaapH7mo=; b=T2ePE/cKae/zGG6w7B//p2Yn8/83O8IzvH9b+/SMHSVBgtU/W2em6bWJnjDN+OvSdE22 v49QGUfrleazDI8lm7x6JbzWynp2B7sxZGIpPNceAeC87ETuvzyLoiSM5jdNLAo3sik4 aoPxdbnAd62H3u5XRRLFmWRTgeXxc47Vypv5IKhLr6ZLfPeCgi325IwHIBj4Pfq5PCgK g5LE95Evhazk8M2WPNV2bjqva1p2PY22IHOGMTw9coZLoet5vVXTAi4awlw+YkBn/hJ8 XSTH2Ngy84eeW0uO+8uVztgoEm+dsPDFyVnQwzmrKqLau0ecoFBJE5cWSkQGXa7faacx /g== Received: from ppma02wdc.us.ibm.com (aa.5b.37a9.ip4.static.sl-reverse.com [169.55.91.170]) by mx0b-001b2d01.pphosted.com (PPS) with ESMTPS id 3g5392rx8q-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 18 May 2022 15:51:29 +0000 Received: from pps.filterd (ppma02wdc.us.ibm.com [127.0.0.1]) by ppma02wdc.us.ibm.com (8.16.1.2/8.16.1.2) with SMTP id 24IFnZUG003184; Wed, 18 May 2022 15:51:28 GMT Received: from b01cxnp22036.gho.pok.ibm.com (b01cxnp22036.gho.pok.ibm.com [9.57.198.26]) by ppma02wdc.us.ibm.com with ESMTP id 3g2429wger-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 18 May 2022 15:51:28 +0000 Received: from b01ledav005.gho.pok.ibm.com (b01ledav005.gho.pok.ibm.com [9.57.199.110]) by b01cxnp22036.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 24IFpSlm12779816 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 18 May 2022 15:51:28 GMT Received: from b01ledav005.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 40BC3AE060; Wed, 18 May 2022 15:51:28 +0000 (GMT) Received: from b01ledav005.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 48FE9AE05F; Wed, 18 May 2022 15:51:27 +0000 (GMT) Received: from [9.163.6.139] (unknown [9.163.6.139]) by b01ledav005.gho.pok.ibm.com (Postfix) with ESMTP; Wed, 18 May 2022 15:51:27 +0000 (GMT) Message-ID: <6d517473-9ac4-8a58-64c5-1c27ecd6f95f@linux.ibm.com> Date: Wed, 18 May 2022 10:51:26 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v2 0/2] iio: humidity: si7020: Check device property for skipping reset in probe Content-Language: en-US From: Eddie James To: Peter Rosin , Jonathan Cameron , devicetree@vger.kernel.org Cc: Jonathan Cameron , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, krzysztof.kozlowski+dt@linaro.org, robh+dt@kernel.org, lars@metafoo.de, miltonm@us.ibm.com, linux-i2c@vger.kernel.org References: <20220512162020.33450-1-eajames@linux.ibm.com> <20220512174859.000042b6@Huawei.com> <4fd44316-689e-1b72-d483-2c617d2a455d@linux.ibm.com> <20220513174531.00007b9b@Huawei.com> <20220514144318.309be1ec@jic23-huawei> <0569bb70-e2dc-de85-268d-30ee7c9491fb@axentia.se> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: Kg_7SlHu9GjMAyDKOhMjl65LN9NYtQPe X-Proofpoint-ORIG-GUID: Kg_7SlHu9GjMAyDKOhMjl65LN9NYtQPe X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.874,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-05-18_05,2022-05-17_02,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 impostorscore=0 suspectscore=0 bulkscore=0 spamscore=0 priorityscore=1501 adultscore=0 malwarescore=0 lowpriorityscore=0 mlxscore=0 mlxlogscore=999 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000 definitions=main-2205180092 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/18/22 10:28, Eddie James wrote: > > On 5/14/22 10:02, Peter Rosin wrote: >> 2022-05-14 at 15:43, Jonathan Cameron wrote: >>> On Sat, 14 May 2022 00:48:51 +0200 >>> Peter Rosin wrote: >>> >>>> Hi! >>>> >>>> 2022-05-13 at 18:45, Jonathan Cameron wrote: >>>>> On Thu, 12 May 2022 12:08:07 -0500 >>>>> Eddie James wrote: >>>>>> On 5/12/22 11:48, Jonathan Cameron wrote: >>>>>>> On Thu, 12 May 2022 11:20:18 -0500 >>>>>>> Eddie James wrote: >>>>>>>> I2C commands issued after the SI7020 is starting up or after reset >>>>>>>> can potentially upset the startup sequence. Therefore, the host >>>>>>>> needs to wait for the startup sequence to finish before issuing >>>>>>>> further i2c commands. This is impractical in cases where the >>>>>>>> SI7020 >>>>>>>> is on a shared bus or behind a mux, which may switch channels at >>>>>>>> any time (generating I2C traffic). Therefore, check for a device >>>>>>>> property that indicates that the driver should skip resetting the >>>>>>>> device when probing. >>>>>>> Why not lock the bus?  It's not ideal, but then not resetting >>>>>>> and hence >>>>>>> potentially ending up in an unknown state isn't great either. >>>>>> >>>>>> Agreed, but locking the bus doesn't work in the case where the >>>>>> chip is >>>>>> behind a mux. The mux core driver deselects the mux immediately >>>>>> after >>>>>> the transfer to reset the si7020, causing some i2c traffic, >>>>>> breaking the >>>>>> si7020. So it would also be a requirement to configure the mux to >>>>>> idle >>>>>> as-is... That's why I went with the optional skipping of the reset. >>>>>> Maybe I should add the bus lock too? >>>>> +Cc Peter and linux-i2c for advice as we should resolve any potential >>>>> issue with the mux side of things rather than hiding it in the driver >>>>> (if possible!) >>>> IIUC, the chip in question cannot handle *any* action on the I2C bus >>>> for 15ms (or so) after a "soft reset", or something bad happens >>>> (or at least may happen). >>>> >>>> If that's the case, then providing a means of skipping the reset is >>>> insufficient. If you don't lock the bus, you would need to *always* >>>> skip the reset, because you don't know for certain if something else >>>> does I2C xfers. >>>> >>>> So, in order to make the soft reset not be totally dangerous even in >>>> a normal non-muxed environment, the bus must be locked for the 15ms. >>>> >>>> However, Eddie is correct in that the I2C mux code may indeed do its >>>> muxing xfer right after the soft reset command. There is currently >>>> no way to avoid that muxing xfer. However, it should be noted that >>>> there are ways to mux an I2C bus without using xfers on the bus >>>> itself, so it's not problematic for *all* mux variants. >>>> >>>> It can be debated if the problem should be worked around with extra >>>> dt properties like this, or if a capability should be added to delay >>>> a trailing muxing xfer. >>>> >>>> I bet there are other broken chips that have drivers that do in fact >>>> lock the bus to give the chip a break, but then it all stumbles >>>> because of the unexpected noise if there's a (wrong kind of) mux in >>>> the mix. >>> Ok, so for now I think we need the bus lock for the reset + either >>> a work around similar to this series, or additions to the i2c mux code >>> to stop it doing a muxing xfer if the bus is locked? >> I think there might be cases where it might be valid to restore the mux >> directly after an xfer even if the mux is externally locked prior to the >> muxed xfer. But I'm not sure? In any case, it will be a bit convoluted >> for the mux code to remember that it might need to restore the mux >> later. And it will get even hairier when multiple levels of muxing is >> considered... >> >> Maybe some kind of hook/callback that could be installed temporarily on >> the I2C adapter that is called right after the "real" xfer, where the >> driver could then make the needed mdelay call? >> >> I.e. >> 1. lock the bus >> 2. install this new hook/callback >> 3. do an unlocked xfer, get notified and call mdelay >> 5. uninstall the hook/callback >> 6. unlock the bus >> >> The hook/callback could be uninstalled automatically on unlock, then >> you would not need to handle multiple notifications. But then again, >> there is probably some existing framework that should be used that >> handles all than neatly and efficiently. > > > Hm, interesting. Sounds a bit complicated, though very flexible. For a > less flexible, but less complex, approch, we could add a i2c_msg flag > that says to do a delay in the core? And then si7020 could just submit > a couple of raw messages rather than smbus... What do you think? Um, nevermind... that would require changes in all the bus drivers. I'll look into implementing the hook/callback. Thanks, Eddie > > > Thanks, > > Eddie > > > >> >> Me waves hand a bit... >> >> Cheers, >> Peter > >