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Sun, 2 Jun 2019 23:25:49 -0500 Received: from DLEE107.ent.ti.com (157.170.170.37) by DLEE106.ent.ti.com (157.170.170.36) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1713.5; Sun, 2 Jun 2019 23:25:48 -0500 Received: from lelv0327.itg.ti.com (10.180.67.183) by DLEE107.ent.ti.com (157.170.170.37) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1713.5 via Frontend Transport; Sun, 2 Jun 2019 23:25:48 -0500 Received: from [172.24.190.233] (ileax41-snat.itg.ti.com [10.172.224.153]) by lelv0327.itg.ti.com (8.15.2/8.15.2) with ESMTP id x534PfNv118820; Sun, 2 Jun 2019 23:25:43 -0500 Subject: Re: [PATCH] PCI: endpoint: Add DMA to Linux PCI EP Framework To: Vinod Koul References: <1558650258-15050-1-git-send-email-alan.mikhak@sifive.com> <305100E33629484CBB767107E4246BBB0A6FAFFD@DE02WEMBXB.internal.synopsys.com> <305100E33629484CBB767107E4246BBB0A6FC308@DE02WEMBXB.internal.synopsys.com> <192e3a19-8b69-dfaf-aa5c-45c7087548cc@ti.com> <20190531050727.GO15118@vkoul-mobl> <20190531063247.GP15118@vkoul-mobl> From: Kishon Vijay Abraham I Message-ID: <400a7c28-39b1-f242-7810-a1d38aa51446@ti.com> Date: Mon, 3 Jun 2019 09:54:20 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190531063247.GP15118@vkoul-mobl> Content-Language: en-US X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190602_212602_573263_503F27DF X-CRM114-Status: GOOD ( 22.98 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "lorenzo.pieralisi@arm.com" , "arnd@arndb.de" , "gregkh@linuxfoundation.org" , Gustavo Pimentel , "palmer@sifive.com" , "kjlu@umn.edu" , "linux-kernel@vger.kernel.org" , "bhelgaas@google.com" , Alan Mikhak , "paul.walmsley@sifive.com" , "linux-pci@vger.kernel.org" , "jingoohan1@gmail.com" , "linux-riscv@lists.infradead.org" , "wen.yang99@zte.com.cn" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org Hi Vinod, On 31/05/19 12:02 PM, Vinod Koul wrote: > On 31-05-19, 10:50, Kishon Vijay Abraham I wrote: >> Hi Vinod, >> >> On 31/05/19 10:37 AM, Vinod Koul wrote: >>> Hi Kishon, >>> >>> On 30-05-19, 11:16, Kishon Vijay Abraham I wrote: >>>> +Vinod Koul >>>> >>>> Hi, >>>> >>>> On 30/05/19 4:07 AM, Alan Mikhak wrote: >>>>> On Mon, May 27, 2019 at 2:09 AM Gustavo Pimentel >>>>> wrote: >>>>>> >>>>>> On Fri, May 24, 2019 at 20:42:43, Alan Mikhak >>>>>> wrote: >>>>>> >>>>>> Hi Alan, >>>>>> >>>>>>> On Fri, May 24, 2019 at 1:59 AM Gustavo Pimentel >>>>>>> wrote: >>>>>>>> >>>>>>>> Hi Alan, >>>>>>>> >>>>>>>> This patch implementation is very HW implementation dependent and >>>>>>>> requires the DMA to exposed through PCIe BARs, which aren't always the >>>>>>>> case. Besides, you are defining some control bits on >>>>>>>> include/linux/pci-epc.h that may not have any meaning to other types of >>>>>>>> DMA. >>>>>>>> >>>>>>>> I don't think this was what Kishon had in mind when he developed the >>>>>>>> pcitest, but let see what Kishon was to say about it. >>>>>>>> >>>>>>>> I've developed a DMA driver for DWC PCI using Linux Kernel DMAengine API >>>>>>>> and which I submitted some days ago. >>>>>>>> By having a DMA driver which implemented using DMAengine API, means the >>>>>>>> pcitest can use the DMAengine client API, which will be completely >>>>>>>> generic to any other DMA implementation. >>>> >>>> right, my initial thought process was to use only dmaengine APIs in >>>> pci-epf-test so that the system DMA or DMA within the PCIe controller can be >>>> used transparently. But can we register DMA within the PCIe controller to the >>>> DMA subsystem? AFAIK only system DMA should register with the DMA subsystem. >>>> (ADMA in SDHCI doesn't use dmaengine). Vinod Koul can confirm. >>> >>> So would this DMA be dedicated for PCI and all PCI devices on the bus? >> >> Yes, this DMA will be used only by PCI ($patch is w.r.t PCIe device mode. So >> all endpoint functions both physical and virtual functions will use the DMA in >> the controller). >>> If so I do not see a reason why this cannot be using dmaengine. The use >> >> Thanks for clarifying. I was under the impression any DMA within a peripheral >> controller shouldn't use DMAengine. > > That is indeed a correct assumption. The dmaengine helps in cases where > we have a dma controller with multiple users, for a single user case it > might be overhead to setup dma driver and then use it thru framework. > > Someone needs to see the benefit and cost of using the framework and > decide. The DMA within the endpoint controller can indeed be used by multiple users for e.g in the case of multi function EP devices or SR-IOV devices, all the function drivers can use the DMA in the endpoint controller. I think it makes sense to use dmaengine for DMA within the endpoint controller. > >>> case would be memcpy for DMA right or mem to device (vice versa) transfers? >> >> The device is memory mapped so it would be only memcopy. >>> >>> Btw many driver in sdhci do use dmaengine APIs and yes we are missing >>> support in framework than individual drivers >> >> I think dmaengine APIs is used only when the platform uses system DMA and not >> ADMA within the SDHCI controller. IOW there is no dma_async_device_register() >> to register ADMA in SDHCI with DMA subsystem. > > We are looking it from the different point of view. You are looking for > dmaengine drivers in that (which would be in drivers/dma/) and I am > pointing to users of dmaengine in that. > > So the users in mmc would be ones using dmaengine APIs: > $git grep -l dmaengine_prep_* drivers/mmc/ > > which tells me 17 drivers! right. For the endpoint case, drivers/pci/controller should register with the dmaengine i.e if the controller has aN embedded DMA (I think it should be okay to keep that in drivers/pci/controller itself instead of drivers/dma) and drivers/pci/endpoint/functions/ should use dmaengine API's (Depending on the platform, this will either use system DMA or DMA within the PCI controller). Thanks Kishon _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv