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

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Date:   Fri, 19 Oct 2018 10:32:24 +1100
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Vinod <vkoul@...nel.org>
Cc:     "sudheer.v" <open.sudheer@...il.com>,
        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 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.
> > 
> > 
> > > While doing resubmission please take some time to understand subsystem
> > > tags to use. (hint git log <subsystem> will tell you)
> > > 
> > > Also series has [[PATCH] 8/9] whereas it should be [PATCH 8/9] please
> > > let git generate that for you (hint git format-patch start..end does a
> > > good job)
> > > 
> > > > @@ -0,0 +1,1594 @@
> > > > +// SPDX-License-Identifier: GPL-2.0
> > > > +/*
> > > > + *   drivers/tty/serial/8250/8250_aspeed_uart_dma.c
> > > > + *    1. 2018/07/01 Shivah Shankar created
> > > > + *    2. 2018/08/25 sudheer.veliseti<open.sudheer@...il.com> modified
> > > 
> > > we dont use this log in kernel. I do not see s-o-b by Shivah, that
> > > should be added. I think he should be author and you need to list
> > > changes you did..
> > > 
> 
>