From mboxrd@z Thu Jan  1 00:00:00 1970
From: "sudheer.v" <open.sudheer@gmail.com>
Subject: Re: [[PATCH] 8/9] DMA-UART-Driver-for-AST2500
Date: Fri, 19 Oct 2018 12:41:56 +0530
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Vinod <vkoul@kernel.org>, Rob Herring <robh+dt@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Joel Stanley <joel@jms.id.au>, Andrew Jeffery <andrew@aj.id.au>, Russell King <linux@armlinux.org.uk>, Dan Williams <dan.j.williams@intel.com>, Jiri Slaby <jslaby@suse.com>, Thomas Gleixner <tglx@linutronix.de>, Marc Zyngier <marc.zyngier@arm.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Michael Moese <mmoese@suse.de>, Hendrik Brueckner <brueckner@linux.vnet.ibm.com>, Kate Stewart <kstewart@linuxfoundation.org>, Philippe Ombredanne <pombredanne@nexb.com>, dmaengine@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradea
List-Id: devicetree@vger.kernel.org

On Fri, Oct 19, 2018 at 10:32:24AM +1100, Benjamin Herrenschmidt wrote:
> On Thu, 2018-10-18 at 15:25 +0530, Vinod wrote:
> > 
> > > It's not a dmaengine driver. It's a serial UART driver that happens to
> > > use a dedicated DMA engine.
> > 
> > Then I see no reason for it to use dmaengine APIs. The framework allows
> > people to share a controller for many clients, but if you have dedicated
> > one then you may use it directly
> 
> Well... the engine is shared by a few UARTs, they have dedicated rings
> but there's a common set of regs for interrupt handling etc.
> 
> That said, I still think it could be contained within a UART driver,
> there's little benefit in adding the framework overhead, esp since
> these are really weak cores, any overhead will be felt.
> 
> Ben.
> 
> > > It's unclear whether it should be split into two drivers, or just have
> > > the serial driver directly use the dma engine since that engine is
> > > dedicated in HW to only work on those UARTs and nothing else...
> > > 
> > > Cheers,
> > > Ben.

Initially we wanted to have  a single driver,
however we had an informal discussion with one of the maintainer 
and based on the feedback, followed the Linux DMA and UART architecture.

If this seperate DMA-engine driver adds more overhead than benifit,
we will merge them into a single UART driver and resubmitt the patches.
Vinod,
      can this dma-controller driver sit under dma subsystem?.
      or better to move it under UART framework.

Thank you.
-- Sudheer