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 622A9C001DF for ; Tue, 1 Aug 2023 16:55:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233319AbjHAQzC (ORCPT ); Tue, 1 Aug 2023 12:55:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233232AbjHAQyz (ORCPT ); Tue, 1 Aug 2023 12:54:55 -0400 Received: from relay8-d.mail.gandi.net (relay8-d.mail.gandi.net [217.70.183.201]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 349272684 for ; Tue, 1 Aug 2023 09:54:52 -0700 (PDT) Received: by mail.gandi.net (Postfix) with ESMTPSA id 5A0151BF203; Tue, 1 Aug 2023 16:54:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1690908891; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=V3jHMGbJP3QoNz+rczliCDsMkczh5HGRrxCqzcgnveo=; b=L0LEpiaWM546go+iQHmp9rh1i2Yg5K61mkwNPerpxzqAlx4f3khZ4bJBL6iFmQZEjCi+xU YsEUV/68G6Vp9+N9YN4AeLybuk44fWbn9SI0V+8G1y56B7QP/QfgAih+WGwJj8+nVirCQ5 OK1qaFJF2FKFGawoxH1xcJmiUSc4z7B1EmqoOk/DSmKga840HiaS9stCveYL1tbT08E/xr hTPxaNpmChcxpLwAmwz29vfS6KemfblRl3lOJ+fVRrhKZLu7pq5BJh08BIkdZUgPjJoj6+ GVzPYq4Ha4IxkoWi5HWU2hAvi4Yl5B8kdp9HTMfufH/4rg9UCmV+fzpaAqBQ6Q== Date: Tue, 1 Aug 2023 18:54:49 +0200 From: Miquel Raynal To: Greg Kroah-Hartman Cc: Srinivas Kandagatla , linux-kernel@vger.kernel.org, Thomas Petazzoni , Robert Marko , Luka Perkov , Michael Walle , Randy Dunlap Subject: Re: [PATCH v6 3/3] nvmem: core: Expose cells through sysfs Message-ID: <20230801185449.5088c8d4@xps-13> In-Reply-To: <2023080125-renovate-uptake-86f0@gregkh> References: <20230717075147.43326-1-miquel.raynal@bootlin.com> <20230717075147.43326-4-miquel.raynal@bootlin.com> <2023071717-channel-supernova-4cc9@gregkh> <20230717183323.49a55ad0@xps-13> <2023071724-twiddling-morale-157e@gregkh> <20230731164642.49fea651@xps-13> <2023080125-renovate-uptake-86f0@gregkh> Organization: Bootlin X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-GND-Sasl: miquel.raynal@bootlin.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Greg, gregkh@linuxfoundation.org wrote on Tue, 1 Aug 2023 11:56:40 +0200: > On Mon, Jul 31, 2023 at 05:33:13PM +0200, Miquel Raynal wrote: > > Hi Greg, > >=20 > > gregkh@linuxfoundation.org wrote on Mon, 17 Jul 2023 18:59:52 +0200: > > =20 > > > On Mon, Jul 17, 2023 at 06:33:23PM +0200, Miquel Raynal wrote: =20 > > > > Hi Greg, > > > >=20 > > > > gregkh@linuxfoundation.org wrote on Mon, 17 Jul 2023 16:32:09 +0200: > > > > =20 > > > > > On Mon, Jul 17, 2023 at 09:51:47AM +0200, Miquel Raynal wrote: = =20 > > > > > > The binary content of nvmem devices is available to the user so= in the > > > > > > easiest cases, finding the content of a cell is rather easy as = it is > > > > > > just a matter of looking at a known and fixed offset. However, = nvmem > > > > > > layouts have been recently introduced to cope with more advanced > > > > > > situations, where the offset and size of the cells is not known= in > > > > > > advance or is dynamic. When using layouts, more advanced parser= s are > > > > > > used by the kernel in order to give direct access to the conten= t of each > > > > > > cell, regardless of its position/size in the underlying > > > > > > device. Unfortunately, these information are not accessible by = users, > > > > > > unless by fully re-implementing the parser logic in userland. > > > > > >=20 > > > > > > Let's expose the cells and their content through sysfs to avoid= these > > > > > > situations. Of course the relevant NVMEM sysfs Kconfig option m= ust be > > > > > > enabled for this support to be available. > > > > > >=20 > > > > > > Not all nvmem devices expose cells. Indeed, the .bin_attrs attr= ibute > > > > > > group member will be filled at runtime only when relevant and w= ill > > > > > > remain empty otherwise. In this case, as the cells attribute gr= oup will > > > > > > be empty, it will not lead to any additional folder/file creati= on. > > > > > >=20 > > > > > > Exposed cells are read-only. There is, in practice, everything = in the > > > > > > core to support a write path, but as I don't see any need for t= hat, I > > > > > > prefer to keep the interface simple (and probably safer). The i= nterface > > > > > > is documented as being in the "testing" state which means we ca= n later > > > > > > add a write attribute if though relevant. > > > > > >=20 > > > > > > There is one limitation though: if a layout is built as a modul= e but is > > > > > > not properly installed in the system and loaded manually with i= nsmod > > > > > > while the nvmem device driver was built-in, the cells won't app= ear in > > > > > > sysfs. But if done like that, the cells won't be usable by the = built-in > > > > > > kernel drivers anyway. =20 > > > > >=20 > > > > > Wait, what? That should not be an issue here, if so, then this c= hange > > > > > is not correct and should be fixed as this is NOT an issue for sy= sfs > > > > > (otherwise the whole tree wouldn't work.) > > > > >=20 > > > > > Please fix up your dependancies if this is somehow not working pr= operly. =20 > > > >=20 > > > > I'm not sure I fully get your point. > > > >=20 > > > > There is no way we can describe any dependency between a storage de= vice > > > > driver and an nvmem layout. NVMEM is a pure software abstraction, t= he > > > > layout that will be chosen depends on the device tree, but if the > > > > layout has not been installed, there is no existing mechanism in > > > > the kernel to prevent it from being loaded (how do you know it's > > > > not on purpose?). =20 > > >=20 > > > Once a layout has been loaded, the sysfs files should show up, right? > > > Otherwise what does a "layout" do? (hint, I have no idea, it's an odd > > > term to me...) =20 > >=20 > > Sorry for the latency in responding to these questions, I'll try to > > clarify the situation. > >=20 > > We have: > > - device drivers (like NAND flashes, SPI-NOR flashes or EEPROMs) which > > typically probe and register their devices into the nvmem > > layer to expose their content through NVMEM. > > - each registration in NVMEM leads to the creation of the relevant > > NVMEM cells which can then be used by other device drivers > > (typically: a network controller retrieving a MAC address from an > > EEPROM through the generic NVMEM abstraction). =20 >=20 >=20 > So is a "cell" here a device in the device model? Or something else? It is not a device in the device model, but I am wondering if it should not be one actually. I discussed with Rafal about another issue in the current design (dependence over a layout driver which might defer forever a storage device probe) which might be solved if the core was handling these layouts differently. > > We recently covered a slightly new case: the NVMEM cells can be in > > random places in the storage devices so we need a "dynamic" way to > > discover them: this is the purpose of the NVMEM layouts. We know cell X > > is in the device, we just don't know where it is exactly at compile > > time, the layout driver will discover it dynamically for us at runtime.= =20 >=20 > So you then create the needed device when it is found? We don't create devices, but we match the layouts with the NVMEM devices thanks to the of_ logic. > > While the "static cells" parser is built-in the NVMEM subsystem, you > > explicitly asked to have the layouts modularized. This means > > registering a storage device in nvmem while no layout driver has been > > inserted yet is now a scenario. We cannot describe any dependency > > between a storage device and a layout driver. We cannot defer the probe > > either because device drivers which don't get access to their NVMEM > > cell are responsible of choosing what to do (most of the time, the idea > > is to fallback to a default value to avoid failing the probe for no > > reason). > >=20 > > So to answer your original question: > > =20 > > > Once a layout has been loaded, the sysfs files should show up, right?= =20 > >=20 > > No. The layouts are kind of "libraries" that the NVMEM subsystem uses > > to try exposing cells *when* a new device is registered in NVMEM (not > > later). The registration of an NVMEM layout does not trigger any new > > parsing, because that is not how the NVMEM subsystem was designed. =20 >=20 > So they are a type of "class" right? Why not just use class devices > then? >=20 > > I must emphasize that if the layout driver is installed in > > /lib/modules/ there is no problem, it will be loaded with > > usermodehelper. But if it is not, we can very well have the layout > > driver inserted after, and this case, while in practice possible, is > > irrelevant from a driver standpoint. It does not make any sense to have > > these cells created "after" because they are mostly used during probes. > > An easy workaround would be to unregister/register again the underlying > > storage device driver. =20 >=20 > We really do not support any situation where a module is NOT in the > proper place when device discovery happens. Great, I didn't know. Then there is no issue. > So this shouldn't be an > issue, yet you all mention it? So how is it happening? Just transparency, I'm giving all details I can. I'll try to come with something slightly different than what we have with the current approach. Thanks, Miqu=C3=A8l