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 E3B82C32772 for ; Tue, 23 Aug 2022 09:42:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242861AbiHWJmF (ORCPT ); Tue, 23 Aug 2022 05:42:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53338 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351651AbiHWJj6 (ORCPT ); Tue, 23 Aug 2022 05:39:58 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0EC6C42AE7; Tue, 23 Aug 2022 01:41:23 -0700 (PDT) Received: from [10.3.2.13] (zone.collabora.co.uk [167.235.23.81]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: dmitry.osipenko) by madras.collabora.co.uk (Postfix) with ESMTPSA id 9A9CB660035D; Tue, 23 Aug 2022 09:40:01 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1661244002; bh=ZlOOvApFGOMbPEfDLhpmrwlUuzkzliB2kc8cG9m2hAg=; h=Date:Subject:To:References:From:In-Reply-To:From; b=GGpm6cPToGVjt2TGPzDVJggwpmq33yQmIW/tSS7VUXeTRxiX7iAGnXdAP7p8t7v2k AU1lXN3llCeQoREhm59iyYyL25HiRUsz1EUv3K/0/1DkHpgIrG+qvOZkIYpLv7u16F NcbfYIiuU/Y+oGUiEGPLqoM5bgT1IaHbczVevsOvMyh1in620AwNkB2FXKOHaI7T2W VY073ruGl62M7bSH/m1bgLwpxeFDX8y1/CFpO+zczh0adSWeGSMVaGlmBu4hCabqrw oBzARqDj9ActJfLP1p0A+K7+A6avRKpOytE6V6k9/3WA8R4nhJ5C6g/0IPEYGkXDPh 3J8NJFPvjGj1w== Message-ID: Date: Tue, 23 Aug 2022 11:39:56 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH RESEND 1/2] i2c: tegra: Add GPCDMA support Content-Language: en-US To: Akhil R , Dmitry Osipenko , "robh+dt@kernel.org" , "devicetree@vger.kernel.org" , "christian.koenig@amd.com" , Jonathan Hunter , Laxman Dewangan , "linux-i2c@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-tegra@vger.kernel.org" , "sumit.semwal@linaro.org" , "thierry.reding@gmail.com" , "wsa@kernel.org" References: <20220819122313.40445-1-akhilrajeev@nvidia.com> <20220819122313.40445-2-akhilrajeev@nvidia.com> <20281ca7-e597-7030-4861-5f9a3594726d@gmail.com> <89a746fd-a98e-3147-7811-33c5051c2b6d@gmail.com> From: Dmitry Osipenko In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/23/22 08:17, Akhil R wrote: >> 22.08.2022 23:33, Dmitry Osipenko пишет: >>> 22.08.2022 13:29, Akhil R пишет: >>>>> On 8/22/22 09:56, Akhil R wrote: >>>>>>> 19.08.2022 18:15, Dmitry Osipenko пишет: >>>>>>>> 19.08.2022 15:23, Akhil R пишет: >>>>>>>>> if (of_device_is_compatible(np, "nvidia,tegra210-i2c-vi")) >>>>>>>>> i2c_dev->is_vi = true; >>>>>>>>> + else >>>>>>>>> + i2c_dev->dma_support = !!(of_find_property(np, "dmas", >>>>>>>>> + NULL)); >>>>>>>> >>>>>>>> 1. You leak the np returned by of_find_property(). >>>>>>>> >>>>>>>> 2. There is device_property_read_bool() for this kind of >>>>>>>> property-exists checks. >>>>>> Okay. I went by the implementation in of_dma_request_slave_channel() to >>>>>> check 'dmas'. >>>>>> >>>>>>>> >>>>>>>> 3. If "dmas" is missing in DT, then dma_request_chan() should return >>>>>>>> NULL and everything will work fine. I suppose you haven't tried to >>>>>>>> test this code. >>>>>>> >>>>>>> Although, no. It should return ERR_PTR(-ENODEV) and then you should >> check >>>>>>> the return code. >>>>>> Yes. Agree that it is more agnostic to check for ERR_PTR(-ENODEV). But >> since I >>>>>> call tegra_init_dma() for every large transfer until DMA is initialized, >> wouldn't >>>>>> it be better to have a flag inside the driver so that we do not have to go >>>>> through >>>>>> so many functions for every attempted DMA transaction to find out that >> the >>>>> DT >>>>>> properties don't exist? >>>>>> >>>>>> Shall I just put i2c_dev->dma_support = true here since DMA is supported >> by >>>>>> hardware? It would turn false if dma_request_chan() returns something >> other >>>>>> than -EPROBE_DEFER. >>>>>> >>>>>> if (of_device_is_compatible(np, "nvidia,tegra210-i2c-vi")) >>>>>> i2c_dev->is_vi = true; >>>>>> + else >>>>>> + i2c_dev->dma_support = true; >>>>> >>>>> The code already has dma_mode for that. I don't see why another variable >>>>> is needed. >>>>> >>>>> Either add new generic dma_request_chan_optional() that will return NULL >>>>> if channel is not available and make Tegra I2C driver to use it, or >>>>> handle the error code returned by dma_request_chan(). >>>> >>>> Let me elaborate my thoughts. >>>> >>>> The function tegra_i2c_init_dma() is also called inside tegra_i2c_xfer_msg() if >>>> DMA is not initialized before, i.e. if (!i2c_dev->dma_buf). >>> >>> This is not true >>> >>> i2c_dev->dma_mode=false if !i2c_dev->dma_buf and that's it >>> >>> https://elixir.bootlin.com/linux/v6.0-rc2/source/drivers/i2c/busses/i2c- >> tegra.c#L1253 >>> >>> tegra_i2c_init_dma() is invoked only during probe >>> >>>> So, if suppose there is no DT entry for dmas, the driver would have to go take >> the >>>> path tegra_i2c_init_dma() -> dma_request_chan() -> of_*() apis -> ... and >> then figure >>>> out that DMA is not supported. This would happen for each transfer of size >> larger than >>>> I2C_PIO_MODE_PREFERRED_LEN. >>>> >>>> To avoid this, I am looking for a variable/flag which can indicate if the driver >> should attempt >>>> to configure DMA or not. I didn't quite get the idea if dma_mode can be >> extended to support >>>> this, because it is updated based on xfer_size on each transfer. My idea of >> i2c_dev->dma_support >>>> is that it will be constant after the probe(). >> >> I see now that it's you added tegra_i2c_init_dma() to >> tegra_i2c_xfer_msg(). And tegra_i2c_init_dma() already falls back to PIO >> if DMA is unavailable. >> >> I don't remember why !IS_ENABLED(CONFIG_TEGRA20_APB_DMA) was added >> to >> tegra_i2c_init_dma(), but if dma_request_chan() returns -EPROBE_DEFER >> when there is no DMA channel available at all, then you should fix it. >> >> Trying to initialize DMA during transfer if it failed to initialize >> during probe is a wrong approach. DMA must be initialized only once >> during probe. Please make the probe to work properly. > > What I am trying for is to have a mechanism that doesn't halt the i2c transfers > till DMA is available. Also, I do not want to drop DMA because it was unavailable > during probe(). Why is it unavailable? Sounds like you're not packaging kernel properly. > This situation is sure to hit if we have I2C driver as built in and DMA driver as a > module. In such cases, I2C will never be able to use the DMA. For Tegra I2C built-in + DMA driver module you should add the dma.ko to initramfs and then it will work. This is a common practice for many kernel drivers. It's also similar to a problem with firmware files that must be available to drivers during boot, > Another option I thought about was to request and free DMA channel for each > transfer, which many serial drivers already do. But I am a bit anxious if that will > increase the latency of transfer. Perhaps all you need to do is to add MODULE_SOFTDEP to Tegra I2C driver like we did it for the EMC driver [1]. [1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=14b43c20c283de36131da0cb44f3170b9ffa7630 -- Best regards, Dmitry