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 E7A19C001E0 for ; Mon, 23 Oct 2023 16:26:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233659AbjJWQ0l (ORCPT ); Mon, 23 Oct 2023 12:26:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46014 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232077AbjJWQ0U (ORCPT ); Mon, 23 Oct 2023 12:26:20 -0400 Received: from fllv0015.ext.ti.com (fllv0015.ext.ti.com [198.47.19.141]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1583210A; Mon, 23 Oct 2023 09:26:17 -0700 (PDT) Received: from fllv0034.itg.ti.com ([10.64.40.246]) by fllv0015.ext.ti.com (8.15.2/8.15.2) with ESMTP id 39NGQA8Q064284; Mon, 23 Oct 2023 11:26:10 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ti.com; s=ti-com-17Q1; t=1698078370; bh=ToVUXy/JJet0aGuRbevQ1uj23FQvFLehD2uGhtFjkOw=; h=Date:Subject:To:CC:References:From:In-Reply-To; b=RmPm0XZT1FuQyVBHx2xmRT0GxHgTWos1KfY2lxlHygEGoqcaHpSWdKv1e2+kmGBFm 7jgfTUQttjCnNGdy2nMk9kInpQ/qxe2qBJsniUGyw1p1OcYJA/SygAOBiInmB8EGSM 1VqEDYTtMVlkvSvexR6FEAD6kq4m+wIgY8cr3+0Q= Received: from DLEE114.ent.ti.com (dlee114.ent.ti.com [157.170.170.25]) by fllv0034.itg.ti.com (8.15.2/8.15.2) with ESMTPS id 39NGQAux094084 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 23 Oct 2023 11:26:10 -0500 Received: from DLEE111.ent.ti.com (157.170.170.22) by DLEE114.ent.ti.com (157.170.170.25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2507.23; Mon, 23 Oct 2023 11:26:09 -0500 Received: from lelv0327.itg.ti.com (10.180.67.183) by DLEE111.ent.ti.com (157.170.170.22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2507.23 via Frontend Transport; Mon, 23 Oct 2023 11:26:09 -0500 Received: from [10.250.38.120] (ileaxei01-snat2.itg.ti.com [10.180.69.6]) by lelv0327.itg.ti.com (8.15.2/8.15.2) with ESMTP id 39NGQ9NO063677; Mon, 23 Oct 2023 11:26:09 -0500 Message-ID: <67efff7e-adc5-4117-a715-7fe219d2f92c@ti.com> Date: Mon, 23 Oct 2023 11:26:09 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mux: mmio: use reg property when parent device is not a syscon Content-Language: en-US To: Peter Rosin , Greg Kroah-Hartman , Rob Herring , Krzysztof Kozlowski , Nishanth Menon , Vignesh Raghavendra CC: , References: <20230911151030.71100-1-afd@ti.com> <0cb645c7-f3c5-e4bb-7686-2a83d32274bb@axentia.se> <38d3582f-c2d6-3d1a-5706-84fccd22a2ac@axentia.se> From: Andrew Davis In-Reply-To: <38d3582f-c2d6-3d1a-5706-84fccd22a2ac@axentia.se> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/20/23 4:22 PM, Peter Rosin wrote: > Hi! > > 2023-10-20 at 18:43, Andrew Davis wrote: >> On 10/20/23 9:28 AM, Peter Rosin wrote: >>> Hi! >>> >>> 2023-09-11 at 17:10, Andrew Davis wrote: >>>> The DT binding for the reg-mux compatible states it can be used when the >>>> "parent device of mux controller is not syscon device". It also allows >>>> for a reg property. When the reg property is provided, use that to >>>> identify the address space for this mux. If not provided fallback to >>>> using the parent device as a regmap provider. >>>> >>>> Signed-off-by: Andrew Davis >>>> Reviewed-by: Nishanth Menon >>>> --- >>>> >>>> Changes from v2: >>>>   - Rebased on v6.6-rc1 >>>> >>>> Changes from v1: >>>>   - Flip logic as suggested in v1[0] >>>> >>>> [0] https://lore.kernel.org/lkml/1c27d9d4-b1cc-c158-90f7-f7e47e02c424@ti.com/T/ >>>> >>>>   drivers/mux/mmio.c | 9 ++++++--- >>>>   1 file changed, 6 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/drivers/mux/mmio.c b/drivers/mux/mmio.c >>>> index fd1d121a584ba..b6095b7853ed2 100644 >>>> --- a/drivers/mux/mmio.c >>>> +++ b/drivers/mux/mmio.c >>>> @@ -44,10 +44,13 @@ static int mux_mmio_probe(struct platform_device *pdev) >>>>       int ret; >>>>       int i; >>>>   -    if (of_device_is_compatible(np, "mmio-mux")) >>>> +    if (of_device_is_compatible(np, "mmio-mux")) { >>>>           regmap = syscon_node_to_regmap(np->parent); >>>> -    else >>>> -        regmap = dev_get_regmap(dev->parent, NULL) ?: ERR_PTR(-ENODEV); >>>> +    } else { >>>> +        regmap = device_node_to_regmap(np); >>> >>> I started digging in device_node_to_regmap() to try to find an error that >>> could be used to trigger if the failover to dev_get_regmap() should be >>> tried, instead of always doing the failover on error. I got lost fairly >>> quickly, but it seems device_node_to_regmap() can return -EDEFER_PROBE. >>> While I'm not certain that it is applicable, that case should probably >>> not fall back to dev_get_regmap()... >>> >>> Are there other error cases that should prevent the failover? I would >>> guess that it's perhaps just a single error that should trigger trying >>> the failover path? But I don't know, and which error if that's the case? >>> >> >> Ideally the only error that will be returned is ENOMEM, which happens when >> this node does not have a 'reg' property, and this is also the one case we >> want to do the failover. So all should be well. > > The ideal working case is usually not much of a problem. When I look at what > device_node_to_regmap does, I find, appart from -ENOMEM, possibilities of > -ENOENT (because no clock), and the clock may theoretically fail to prepare > for numerous reasons hidden in clock drivers, but the clock core can > trigger at least -EACCES and -EINPROGRESS via runtime PM. > > And it definitely looks like the -EPROBE_DEFER case needs to be addressed. > I.e., why is this call chain not a problem? > > mux_mmio_probe > ->device_node_to_regmap > -> device_node_get_regmap > -> of_syscon_register > -> of_hwspin_lock_get_id > <- -EPROBE_DEFER > <- ERR_PTR(-EPROBE_DEFER) > <- ERR_PTR(-EPROBE_DEFER) > <- ERR_PTR(-EPROBE_DEFER) > > As far as I can tell, if device_node_to_regmap() fails with -EPROBE_DEFER > with your patch, then mux_mmio_probe() misbehaves. It should have aborted > and failed with -EPROBE_DEFER, but instead throws that error away and > goes on to try dev_get_regmap(). That, in turn, is probably futile and > will likely error out in some way, breaking a system that might have been > ok, if the probe had been retried some time later. > This is why I liked the v1 version, dev_get_regmap() just returns a simple NULL on error, no complex EPROBE_DEFER oddness :) So is EPROBE_DEFER the only one we think should retry and not go down the fallback path? I believe that is the normal assumption for most drivers. > As long as the above is not sufficiently explained away, or fixed, I > consider the patch broken. > >>> How much badness can be caused if syscon_node_to_regmap() fails for some >>> random obscure reason and the failover path is taken inadvertently? It >>> certainly smells bad for -EDEFER_PROBE, but do you have any insight in >>> other cases? >>> >> >> If we take the failover inadvertently then we will check if the parent >> node is a syscon, if it is then our offset will most likely be wrong >> (parent will not match child 'reg'). >> >>> And after getting to approx that point a while back, I had other things >>> to take care of, and this fell off the table. Sorry! >>> >> >> No problem as long as we can find a way to get this in quickly (lot of >> DT warning need cleaned up based on this patch). > > Hold your horses, I need the above explanation first (and perhaps an > updated patch). > I'm not normally so impatient but this went two whole kernel cycles without any comment until rc6.. v4 on the way. Andrew > Cheers, > Peter > >> Thanks >> Andrew >> >>> Cheers, >>> Peter >>> >>>> +        if (IS_ERR(regmap)) >>>> +            regmap = dev_get_regmap(dev->parent, NULL) ?: ERR_PTR(-ENODEV); >>>> +    } >>>>       if (IS_ERR(regmap)) { >>>>           ret = PTR_ERR(regmap); >>>>           dev_err(dev, "failed to get regmap: %d\n", ret);