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 7E066C433FE for ; Mon, 29 Nov 2021 12:58:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237293AbhK2NB1 (ORCPT ); Mon, 29 Nov 2021 08:01:27 -0500 Received: from fllv0016.ext.ti.com ([198.47.19.142]:33958 "EHLO fllv0016.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230372AbhK2M70 (ORCPT ); Mon, 29 Nov 2021 07:59:26 -0500 Received: from fllv0035.itg.ti.com ([10.64.41.0]) by fllv0016.ext.ti.com (8.15.2/8.15.2) with ESMTP id 1ATCtnAa110837; Mon, 29 Nov 2021 06:55:49 -0600 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ti.com; s=ti-com-17Q1; t=1638190549; bh=xpfKTadBXPo99vJqrIrr6yNPN/kKtoRw6ZjKzqOo2hI=; h=Subject:To:CC:References:From:Date:In-Reply-To; b=aE6aURdqJHi/1iX70+u1w8+uoyaES7cZd+u0IG3x0jORKHp8ckasbN8e6FlbNu27x pnEHdVPyEInGT7FMjXyVUYcJg9Boj8vRLbFTd/XecWh8HilAKii+qMYUZI8XCxJtXK vfr+6PiTOgNWIuiljypMtKczAvr//2qoTnkkKh4E= Received: from DLEE103.ent.ti.com (dlee103.ent.ti.com [157.170.170.33]) by fllv0035.itg.ti.com (8.15.2/8.15.2) with ESMTPS id 1ATCtnjG007961 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 29 Nov 2021 06:55:49 -0600 Received: from DLEE115.ent.ti.com (157.170.170.26) by DLEE103.ent.ti.com (157.170.170.33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.14; Mon, 29 Nov 2021 06:55:48 -0600 Received: from lelv0327.itg.ti.com (10.180.67.183) by DLEE115.ent.ti.com (157.170.170.26) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.14 via Frontend Transport; Mon, 29 Nov 2021 06:55:48 -0600 Received: from [10.250.232.185] (ileax41-snat.itg.ti.com [10.172.224.153]) by lelv0327.itg.ti.com (8.15.2/8.15.2) with ESMTP id 1ATCth3Q070706; Mon, 29 Nov 2021 06:55:44 -0600 Subject: Re: [PATCH RFC v3 1/4] dt-bindings: mux: Increase the number of arguments in mux-controls To: Peter Rosin CC: Vignesh Raghavendra , Nishanth Menon , Rob Herring , Wolfgang Grandegger , Marc Kleine-Budde , Kishon Vijay Abraham I , Vinod Koul , , , , References: <20211123081222.27979-1-a-govindraju@ti.com> <20211123081222.27979-2-a-govindraju@ti.com> <24781209-928b-dea4-de0b-b103dac8de82@axentia.se> <5f455c4d-5edb-4382-1193-a519a7a227a5@ti.com> <46644e9a-a9e9-4cdb-47e3-f42ebf49f805@ti.com> <11e3bb89-d706-28c1-b7a5-e61c5cc99c93@axentia.se> From: Aswath Govindraju Message-ID: Date: Mon, 29 Nov 2021 18:25:43 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <11e3bb89-d706-28c1-b7a5-e61c5cc99c93@axentia.se> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Hi Peter, On 29/11/21 5:58 pm, Peter Rosin wrote: > Hi Aswath, > > On 2021-11-29 10:31, Aswath Govindraju wrote: >> Hi Peter, >> >> On 29/11/21 1:45 pm, Peter Rosin wrote: >>> >>> >>> On 2021-11-29 05:36, Aswath Govindraju wrote: >>>> Hi Peter, >>>> >>>> On 25/11/21 7:05 pm, Peter Rosin wrote: >>>>> Hi! >>>>> >>>>> You need to have some description on how #mux-control-cells now work. >>>>> The previous description is in mux-consumer.yaml and an update there >>>>> is needed. >>>>> >>>>> However, I have realized that the adg792a binding uses #mux-control-cells >>>>> to indicate if it should expose its three muxes with one mux-control >>>>> and operate the muxes in parallel, or if it should be expose three >>>>> independent mux-controls. So, the approach in this series to always >>>>> have the #mux-control-cells property fixed at <2> when indicating a >>>>> state will not work for that binding. And I see no fix for that binding >>>>> without adding a new property. >>>>> >>>>> So, I would like a different approach. Since I dislike how mux-controls >>>>> -after this series- is not (always) specifying a mux-control like the name >>>>> says, but instead optionally a specific state, the new property I would >>>>> like to add is #mux-state-cells such that it would always be one more >>>>> than #mux-control-cells. >>>>> >>>>> mux: mux-controller { >>>>> compatible = "gpio-mux"; >>>>> #mux-control-cells = <0>; >>>>> #mux-state-cells = <1>; >>>>> >>>>> mux-gpios = <...>; >>>>> }; >>>>> >>>>> can-phy { >>>>> compatible = "ti,tcan1043"; >>>>> ... >>>>> mux-states = <&mux 1>; >>>>> }; >>>>> >>>>> That solves the naming issue, the unused argument for mux-conrtrollers >>>>> that previously had #mux-control-cells = <0>, and the binding for adg792a >>>>> need no longer be inconsistent. >>>>> >>>>> Or, how should this be solved? I'm sure there are other options... >>>>> >>>> >>>> >>>> I feel that the new approach using mux-state-cells seems to be >>>> overpopulating the device tree nodes, when the state can be represented >>>> using the control cells. I understand that the definition for >>>> mux-controls is to only specify the control line to be used in a given >>>> mux. Can't it now be upgraded to also represent the state at which the >>>> control line has to be set to? >>>> >>>> With respect to adg792a, it is inline with the current implementation >>>> and the only change I think would be required in the driver is, >>> >>> No, that does not work. See below. >>> >>>> >>>> diff --git a/drivers/mux/adg792a.c b/drivers/mux/adg792a.c >>>> index e8fc2fc1ab09..2cd3bb8a40d4 100644 >>>> --- a/drivers/mux/adg792a.c >>>> +++ b/drivers/mux/adg792a.c >>>> @@ -73,8 +73,6 @@ static int adg792a_probe(struct i2c_client *i2c) >>>> ret = device_property_read_u32(dev, "#mux-control-cells", &cells); >>>> if (ret < 0) >>>> return ret; >>>> - if (cells >= 2) >>>> - return -EINVAL; >>>> >>>> mux_chip = devm_mux_chip_alloc(dev, cells ? 3 : 1, 0); >>> >>> When you add cell #2 with the state, the cells variable will end up >>> as 2 always. Which means that there is no way to alloc one mux >>> control since "cells ? 3 : 1" will always end up as "3", with no >>> easy fix. >>> >>> So, your approach does not work for this driver. >>> >> >> Sorry, but how is this different from the case of >> >> #mux-control-cells = 1 >> >> If #mux-control-cells is equal to 1 it means the consumer will use a >> given control line from the mux chip. The same would be the case when we >> will be using, #mux-control-cells is equal to 2, except we can also >> provide the state. >> >> If the consumer will use all the lines then #mux-control-cells will be >> set to 0. In this condition the state can't be provided from the DT and >> the consumer will be controlling the entire mux chip. If >> #mux-control-cells is greater than 0 then we will not be able to provide >> multiple lines of control using a single mux-controls entry(mux-controls >> = <...>;) right? We would have the using multiple mux-controls >> entries(mux-controls = <...>, <...>;). > > I think you misunderstand. The adg792a driver operates the chip in > different modes depending on if you specify 0 or 1 cells. With 0, > it's not just that the consumer operates three muxes. It is also, and > more importantly, that the three muxes are operated in parallel without > the consumer doing anything different with the single mux control it > sees (even if there are three muxes operated by that single mux > control). > > That said, yes, you can make it limp along like you describe above. > But why should it not be possible to specify a specific state when > the adg792a driver operates the muxes in parallel? And yes, you could > add some other flag to indicate this mode, but my point is that it > is silly to add special cases like this if you don't need to. Since > adding a specific state is the new thing, that is what should be > added in a way that fits with the old stuff without imposing new > flags on that old stuff. > > An example: the three muxes in an adg792a chip could be used as > two muxes for some I2C bus (SCL and SDA signals) and the third mux > for something unrelated. Suppose that you want to operate the adg792a > as three parallel muxes so that you mux SCL and SDA simultaneously > (as is expected by the i2c-mux-gpmux binding, it only expects one > mux control), and that you want to use the third mux as the enable- > state for your phy. With your suggested binding you cannot, unless > you add a mechanism to make the adg792a driver operate its muxes in > parallel even if there are two cells instead of zero. I.e. without > that new flag the i2c-mux-gpmux binding needs to see > > #mux-control-cells = <0>; > > while your new phy binding instead needs to see > > #mux-control-cells = <2>; > > And you obviously can't have it both ways. > > (Sure, it would not be possible to mux the I2C bus while the phy > is enabled in the above example, but there could be some other > limitation in place that makes that invalid anyway. And it's just > an example anyway...) > > A mux-control is potentially a shared resource, and bindings have > to take this into account. > Understood. Thank you for the explanation. Will correct the implementation and post a respin. Regards, Aswath > Cheers, > Peter >