Re: [[PATCH] 8/9] DMA-UART-Driver-for-AST2500

From: "sudheer.v" <open.sudheer@gmail.com>
To: Vinod <vkoul@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.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.infradead.org,
	linux-aspeed@lists.ozlabs.org,
	Sudheer V <sudheer.veliseti@aspeedtech.com>,
	ShivahShankar Shakarnarayan rao 
	<shivahshankar.shankarnarayanrao@aspeedtech.com>
Subject: Re: [[PATCH] 8/9] DMA-UART-Driver-for-AST2500
Date: Fri, 26 Oct 2018 12:37:28 +0530	[thread overview]
Message-ID: <20181026070726.GA30088@Pilot130> (raw)
In-Reply-To: <20181020162624.GC2894@vkoul-mobl>

On Sat, Oct 20, 2018 at 09:56:24PM +0530, Vinod wrote:
> On 19-10-18, 12:41, sudheer.v wrote:
> > 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.
> 
> 
> My advise would be to see what you can do with the DMA IP block. If this
> can/would be used in different places then it would make sense to do a
> dmaengine driver and solve the problem for everyone.
> 
> If this is always going to be hidden behind serial then maybe it makes
> sense to be inside serial driver and not use dmaengine APIs
> 
> If you decide to prefer the former case, please move it to dmaengine and
> resubmit :)
> 
> HTH
> -- 
> ~Vinod

Hi All,
 As the DMA engine is dedicated only to UART,we have decided 
 to rewrite the driver so that no code will come under 
 drivers/dma.

 I will resubmitt the patches after merging dma controller
 code and uart driver code.
Regards
-sudheer