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

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Message-ID: <20181026070726.GA30088@Pilot130>
Date:   Fri, 26 Oct 2018 12:37:28 +0530
From:   "sudheer.v" <open.sudheer@...il.com>
To:     Vinod <vkoul@...nel.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Russell King <linux@...linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Jiri Slaby <jslaby@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Michael Moese <mmoese@...e.de>,
        Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org,
        Sudheer V <sudheer.veliseti@...eedtech.com>,
        ShivahShankar Shakarnarayan rao 
        <shivahshankar.shankarnarayanrao@...eedtech.com>
Subject: Re: [[PATCH] 8/9] DMA-UART-Driver-for-AST2500

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