From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com [115.124.30.132]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B99DE1BDCE; Tue, 19 Dec 2023 07:00:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R691e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046060;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0Vyq-RHH_1702969201; Received: from 30.97.48.48(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Vyq-RHH_1702969201) by smtp.aliyun-inc.com; Tue, 19 Dec 2023 15:00:01 +0800 Message-ID: <1b9a7d11-c91f-4b55-bf27-d7c703ed5c24@linux.alibaba.com> Date: Tue, 19 Dec 2023 15:00:24 +0800 Precedence: bulk X-Mailing-List: dmaengine@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] dmaengine: sprd: delete enable opreation in probe To: liu kaiwei , Vinod Koul Cc: Kaiwei Liu , Orson Zhai , Chunyan Zhang , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, Wenming Wu References: <20231102121623.31924-1-kaiwei.liu@unisoc.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 12/19/2023 1:21 PM, liu kaiwei wrote: > On Mon, Dec 11, 2023 at 7:41 PM Vinod Koul wrote: >> >> On 06-12-23, 17:32, liu kaiwei wrote: >>> On Fri, Nov 24, 2023 at 9:11 PM Vinod Koul wrote: >>>> >>>> On 02-11-23, 20:16, Kaiwei Liu wrote: >>>>> From: "kaiwei.liu" >>>> >>>> Typo is subject line >>>> >>>>> >>>>> In the probe of dma, it will allocate device memory and do some >>>>> initalization settings. All operations are only at the software >>>>> level and don't need the DMA hardware power on. It doesn't need >>>>> to resume the device and set the device active as well. here >>>>> delete unnecessary operation. >>>> >>>> Don't you need to read or write to the device? Without enable that wont >>>> work right? >>>> >>> >>> Yes, it doesn't need to read or write to the device in the probe of DMA. >>> We will enable the DMA when allocating the DMA channel. >> >> So you will probe even if device is not present! I think it makes sense >> to access device registers in probe! > > There is another reason why we delete enable/disable and not to access > device in probe. The current driver is applicable to two DMA devices > in different > power domain. For some scenes, one of the domain is power off and when you > probe, enable the dma with the domain power off may cause crash. > > For example, one case is for audio co-processor and DMA serves for it, > DMA's power domain is off during initialization since audio is not used > at that time, so we cannot read/write DMA's register for this kind of cases. > > @Baolin Wang > Hi baolin，what's your opinion? Please add your explanation into the commit message. Moreover, I think Vinod's concern is reasonable, so you can not move the pm_runtime_enable() after registering the devices, which means users can access the device without powering on. To solve your problem, I think you can move the pm_runtime_enable() before dma_async_device_register(), then if users want to use DMA in probe stage, the dma_chan_get()--->sprd_dma_alloc_chan_resources() will help to power on it.