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From: Kishon Vijay Abraham I <kishon@ti.com>
To: Arnd Bergmann <arnd@arndb.de>, Vinod Koul <vkoul@kernel.org>
Cc: Alan Mikhak <alan.mikhak@sifive.com>,
	Gustavo Pimentel <Gustavo.Pimentel@synopsys.com>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"jingoohan1@gmail.com" <jingoohan1@gmail.com>,
	"bhelgaas@google.com" <bhelgaas@google.com>,
	"wen.yang99@zte.com.cn" <wen.yang99@zte.com.cn>,
	"kjlu@umn.edu" <kjlu@umn.edu>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>,
	"palmer@sifive.com" <palmer@sifive.com>,
	"paul.walmsley@sifive.com" <paul.walmsley@sifive.com>
Subject: Re: [PATCH] PCI: endpoint: Add DMA to Linux PCI EP Framework
Date: Mon, 3 Jun 2019 09:59:16 +0530	[thread overview]
Message-ID: <b5d5aa64-710b-3fcc-4197-2a2114266385@ti.com> (raw)
In-Reply-To: <CAK8P3a2jePe7Qfjciq4fdfngAudzCb-cai4fr3_BG_evnbjhvw@mail.gmail.com>

Hi,

On 31/05/19 1:19 PM, Arnd Bergmann wrote:
> On Fri, May 31, 2019 at 8:32 AM Vinod Koul <vkoul@kernel.org> wrote:
>> On 31-05-19, 10:50, Kishon Vijay Abraham I wrote:
>>> On 31/05/19 10:37 AM, Vinod Koul wrote:
>>>> On 30-05-19, 11:16, Kishon Vijay Abraham I wrote:
>>>>>
>>>>> 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.
> 
> I think the main question is about how generalized we want this to be.
> There are lots of difference PCIe endpoint implementations, and in
> case of some licensable IP cores like the designware PCIe there are
> many variants, as each SoC will do the implementation in a slightly
> different way.
> 
> If we can have a single endpoint driver than can either have an
> integrated DMA engine or use an external one, then abstracting that
> DMA engine helps make the driver work more readily either way.
> 
> Similarly, there may be PCIe endpoint implementations that have
> a dedicated DMA engine in them that is not usable for anything else,
> but that is closely related to an IP core we already have a dmaengine
> driver for. In this case, we can avoid duplication.

right. Either way it makes more sense to register DMA embedded within the PCIe
endpoint controller instead of creating epc_ops for DMA transfers.

Thanks
Kishon

  reply	other threads:[~2019-06-03  4:30 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-23 22:24 [PATCH] PCI: endpoint: Add DMA to Linux PCI EP Framework Alan Mikhak
2019-05-24  8:59 ` Gustavo Pimentel
2019-05-24 19:42   ` Alan Mikhak
2019-05-27  9:09     ` Gustavo Pimentel
2019-05-29 22:37       ` Alan Mikhak
2019-05-30  5:46         ` Kishon Vijay Abraham I
2019-05-30 17:56           ` Alan Mikhak
2019-05-31  5:06             ` Kishon Vijay Abraham I
2019-05-31 18:16               ` Alan Mikhak
2019-06-03  4:41                 ` Kishon Vijay Abraham I
2019-06-03 17:42                   ` Alan Mikhak
2019-09-13 12:11                     ` Kishon Vijay Abraham I
2019-09-13 17:39                       ` Alan Mikhak
2019-05-31  5:07           ` Vinod Koul
2019-05-31  5:20             ` Kishon Vijay Abraham I
2019-05-31  6:32               ` Vinod Koul
2019-05-31  7:49                 ` Arnd Bergmann
2019-06-03  4:29                   ` Kishon Vijay Abraham I [this message]
2019-06-03  4:24                 ` Kishon Vijay Abraham I
2019-06-03  4:42                   ` Vinod Koul

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