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 40928C433F5 for ; Mon, 29 Nov 2021 15:49:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245619AbhK2Pwt (ORCPT ); Mon, 29 Nov 2021 10:52:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56428 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232856AbhK2Pus (ORCPT ); Mon, 29 Nov 2021 10:50:48 -0500 Received: from mail-vk1-xa34.google.com (mail-vk1-xa34.google.com [IPv6:2607:f8b0:4864:20::a34]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D8063C09CE65 for ; Mon, 29 Nov 2021 05:56:23 -0800 (PST) Received: by mail-vk1-xa34.google.com with SMTP id u68so11073781vke.11 for ; Mon, 29 Nov 2021 05:56:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Psq6/38akb6pFI4zFrW/zy31oIimVJgvRRtPizriX/8=; b=iyf2Tu45o61YhmukAkmvRRPXYCN8PD/HwC31Ug/gopXsM2RCmehIxo4Hvfchwq9TSQ qbP6BU7S/J7nG+PVQmSHYE2L1/WDNq269HIOar97HUQA8KS2NZjmU8Zh7n2TOd8S+v/a 8RFGSA0/2BM1wgUTEa6UECCiXJC6F7EkwLbkO08oVZtPGuqWTxj9PilPzLcwRn0bUYh0 /YGLbscV7LKxd//FB6z+5lIpr3MCwDvGtc9JXye75J0u2tuMZUwTgaqBVIqHkSMTzxyY vCo+TqQUArbWMYdf0my4u5JXp0f11fotKZjHI3k9XAlrj6Q230YroEBZMxDD0acK7YKn ZF9A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Psq6/38akb6pFI4zFrW/zy31oIimVJgvRRtPizriX/8=; b=sbp48JNf6kUAEIKk6xCgneVhRjgf48TU90RN75LboFVXdqlqnOWoplKfpymGCTwNuA Yb2fa9mn2LhAxpZMmTYf+UHeixMwBs5sfKrEUkRqxnyQ8E4ykUzA6EnVmzeq9YF1AIEB te7aEeG+la0duAAMVrtXVaaRGFnX692rJdeQVdRHk2oqSX8a6M9DLtQ/qIhyP62XZmae MUcHHWf490h8izco81aE/y5kBb6GBz2lBAdSWHsRu0YVvESmrsEiwJOSDAyKAjBZ36lC ZPCULxQ2/0WnrTtPW8MwQFxmHOsST3sPNOSM5W5RwwiHoLdYluUJmIaOe8VvbXQvE2BP Ejvw== X-Gm-Message-State: AOAM532my47TGjjhf5JR3qtubqP3UDXPcfhIfBQi2g7HUQpp+r0h+KyG ceTQkO4KzqNuDRj4+nMXMyAxcj074jI80X9/wUZt5g== X-Google-Smtp-Source: ABdhPJz2HEiIPCArTkwOkAcHR1Mth6V7WDJcoxwiCj0f+X4ZUcus1I83945wLSi2z05M9/rSGgC4ywY2AEmYZ7h08aI= X-Received: by 2002:a05:6122:1306:: with SMTP id e6mr36144108vkp.13.1638194182543; Mon, 29 Nov 2021 05:56:22 -0800 (PST) MIME-Version: 1.0 References: <20211127223253.19098-1-semen.protsenko@linaro.org> In-Reply-To: From: Sam Protsenko Date: Mon, 29 Nov 2021 15:56:10 +0200 Message-ID: Subject: Re: [PATCH 0/8] soc: samsung: Add USIv2 driver To: David Virag Cc: Krzysztof Kozlowski , Rob Herring , Mark Brown , Greg Kroah-Hartman , Jaewon Kim , Chanho Park , Youngmin Nam , devicetree@vger.kernel.org, linux-spi@vger.kernel.org, linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-i2c@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 28 Nov 2021 at 05:15, David Virag wrote: > > On Sun, 2021-11-28 at 00:32 +0200, Sam Protsenko wrote: > > USIv2 IP-core provides selectable serial protocol (UART, SPI or > > High-Speed I2C); only one can be chosen at a time. This series > > implements USIv2 driver, which allows one to select particular USI > > function in device tree, and also performs USI block initialization. > > > > With that driver implemented, it's not needed to do USI > > initialization > > in protocol drivers anymore, so that code is removed from the serial > > driver. > > > > I think the downstream way of doing this (USI node reg being on the > SW_CONF register itself rather than an offset from uart/i2c/spi, the > USI driver only controlling the SW_CONF, and the uart/i2c/spi drivers > controlling their USI_CON and USI_OPTION regs) is cleaner, better, and > easier to adapt to USIv1 too. > One reason why I think it's better to provide SW_CONF register via syscon node, is that it helps us to avoid possible register access conflicts in future, and also conflicts when requesting corresponding resources. In other words, the System Register block can be used by many consumers (drivers) in future; those consumers might try to modify the same registers simultaneously, which might lead to race conditions (as RMW operation is not atomic), so some kind of serialization should be done (like locking in regmap), which is provided by syscon. Also, that wouldn't even come to that: you just can't request the same I/O area twice in Linux. So if SW_CONF is passed via "reg" property to USI driver, and then we try to map the whole System Register (or its portion that includes SW_CONF), that request would fail. Although passing one SW_CONF register via "reg" might look easier to implement, it might also bring us all sort of problems later on. And I think a good design should account for such pitfalls. As for the USI registers: I really don't think that duplicating the code for USI block reset across uart/i2c/spi drivers would help us to accomplish anything. Why those drivers should be even aware of USI reset? At least in USIv2 block, the USI registers and uart/i2c/spi registers are not mixed: they are located at different and always fixed addresses. We can benefit from that fact, and provide Device Tree structure which reflects the hardware one, separating USI control from actual protocol nodes. > For example: I'm sure this is the case on USIv2 devices too, but on > Exynos7885, different devices have USI modes configured differently. > For example a Samsung Galaxy A8 (2018) has all the USI blocks > configured as SPI while a Samsung Galaxy M20 has the first USI > configured as dual HSI2C, the second as HSI2C on the first 2 pins and > the third as HSI2C on the last 2 pins. With this way of doing > everything on USIv2 we'd need 3 disabled USIv2 nodes in the SoC DTSI > for one USI block, each for every protocol the USI block can do, all > having a single child for their protocol and each referencing the same > sysreg (not even sure if that's even supported). Then the board DTS > could enable the USI node it needs. > If I'm following you correctly, then it's not like that. I guess Krzysztof already replied to that, so I'll probably just repeat his words. In that case you'll have something like this in your SoC dtsi (for your USIv1 case of course, because dual HSI2C is not present in USIv2): <<<<<<<<<<<<<<<<<<<<<<<<< cut here >>>>>>>>>>>>>>>>>>>>>>> usi1 { spi1 { }; hsi2c1_1 { }; hsi2c1_2 { }; }; usi2 { spi2 { }; hsi2c2_1 { }; }; usi3 { spi3 { }; hsi2c2_2 { }; }; <<<<<<<<<<<<<<<<<<<<<<<<< cut here >>>>>>>>>>>>>>>>>>>>>>> and then in your board dts you just have to enable corresponding usi's with proper modes, and enable chosen protocol nodes, like this: <<<<<<<<<<<<<<<<<<<<<<<<< cut here >>>>>>>>>>>>>>>>>>>>>>> &usi1 { status = "okay" samsung,mode = ; }; &hsi2c1_1 { status = "okay" }; &hsi2c1_2 { status = "okay" }; <<<<<<<<<<<<<<<<<<<<<<<<< cut here >>>>>>>>>>>>>>>>>>>>>>> > With the downstream way we could have just one USI node and we could > add the 3 protocols it can do disabled as seperate or child nodes. This > way the board DTS only needs to set the appropriate mode setting and > enable the protocol it needs. I'd say much better than having 3 USI > nodes for the same USI block. > Not sure if with downstream USI driver you can actually have protocols as sub-nodes in USI node though. It doesn't do anything like of_platform_populate(). Also, with this USIv2 driver you can do the same thing you described: you can have just one USI node with 3 protocols as sub-nodes (or you can even have protocol nodes outside of USI node, but I'd not recommend that). Actually I can see that it's my fault for not describing that case in bindings example. I'll make sure to do that in v2. You also got me thinking about default mode: sometimes SW_CONF reset value chooses some protocol. In that case maybe it'd useful to have something like USI_V2_DEFAULT, to tell driver to not touch SW_CONF at all. And also I can add USI_V2_NONE while at it, so that driver can write 0x0 to SW_CONF: that way no protocol will be selected. Maybe that can be beneficial for PM reasons, if some board doesn't use some USI blocks at all. Do you think it's feasible to add those two values to dt-bindings header? And is it possible to do so in USIv1? > Also this way is pretty USIv2 centric. Adding USIv1 support to this > driver is difficult this way because of the the lack of USI_CON and > USI_OPTION registers as a whole (so having nowhere to actually set the > reg of the USI node to, as the only thing USIv1 has is the SW_CONF > register). In my opinion being able to use the same driver and same > device tree layout for USIv1 and USIv2 is a definite plus > Well, it's USIv2 driver after all. I never expected it can be extended for USIv1 support. If you think it can be reused for USIv1, it's fine by me. But we need to consider next things: - rename the driver to just "usi.c" (and also its configuration symbol) - provide different compatible for USIv1 (and maybe corresponding driver data) - rework bindings (header and doc); make sure existing bindings are intact (we shouldn't change already introduced interfaces) - in case of USIv1 compatible; don't try to tinker with USIv2 registers - samsung,clkreq-on won't be available in case of USIv1 compatible Because I don't have USIv1 SoC TRM (and neither do I possess some USIv1 board which I can use for test), I don't think it's my place to add USIv1 support. But I think it's possible to do so, using my input above. I can see how it might be frustrating having to do some extra work (comparing to just using the code existing in downstream). But I guess that's the difference: vendor is mostly concerned about competitive advantage and getting to market fast, while upstream is more concerned about quality, considering all use cases, and having proper design. Anyway, we can work together to make it right, and to have both IP-cores support. In the worst case, if those are too different, we can have two separate drivers for those. > The only real drawback of that way is having to add code for USIv2 > inside the UART, HSI2C, and SPI drivers but in my opinion the benefits > overweigh the drawbacks greatly. We could even make the uart/spi/hsi2c > drivers call a helper function in the USI driver to set their USI_CON > and USI_OPTION registers up so that code would be shared and not > duplicated. Wether this patch gets applied like this is not my choice > though, I'll let the people responsible decide > :-) > I'd argue that there are a lot of real drawbacks of using downstream driver as is. That's why I completely re-designed and re-implemented it. Downstream driver can't be built and function as a module, it doesn't respect System Register sharing between consumers, it leads to USI reset code duplication scattered across protocol drivers (that arguably shouldn't even be aware of that), it doesn't reflect HW structure clearly, it's not holding clocks needed for registers access (btw, sysreg clock can be provided in syscon node, exactly for that reason). As Krzysztof said, it also can't handle correct probe order and deferred probes. Downstream driver might work fine for some particular use-cases the vendor has, but in upstream it's better to cover more cases we can expect, as upstream kernel is used on more platforms, with more user space variants, etc. I don't really think protocol drivers should be aware of USI registers at all, but if we they do -- we can provide some API from USIv2 driver later, with EXPORT_SYMBOL(), referencing corresponding USI instance by phandle or using some other mechanism for inter-driver communication. Of course, it's not my place to decide on patch acceptance too. But I was under the impression that maintainers would be ok with this course of actions. Also, upstream kernel seems to already follow the same design for some similar drivers. See for example drivers/soc/qcom/qcom_gsbi.c. > Anyways, soon enough I can write an USIv1 driver after I submit all the > 7885 stuff I'm working on currently. If you want to, you can add USIv2 > support to that driver, or if an USIv2 driver is already in upstream at > that point, if it is written in the downstream way I can add v1 support > to that, or if it's like this I'll have to make a whole seperate driver > with a whole seperate DT structure. > If it's like you said (USIv1 only touches the SW_CONF register), I guess USIv2 driver can be extended for USIv1 case. I already provided my thoughts on such rework above. It's probably better to consult with Krzysztof first. I guess the only way to figure out if it's feasible or it's better to have separate exynos-usi-v1.c for USIv1, is to try and add USIv1 support into USIv2 driver and see how pretty or ugly it is :) Whatever the way you decide to go with, please add me to Cc list when sending USIv1 patches. > Best regards, > David