linux-kernel - RE: [PATCH v5] dma: Add Xilinx AXI Direct Memory Access Engine driver support

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Date:	Thu, 5 Mar 2015 09:34:35 +0000
From:	Appana Durga Kedareswara Rao <appana.durga.rao@...inx.com>
To:	Josh Cartwright <joshc@...com>
CC:	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	Michal Simek <michals@...inx.com>,
	Soren Brinkmann <sorenb@...inx.com>,
	Srikanth Vemula <svemula@...inx.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Srikanth Thokala <sthokal@...inx.com>,
	Anirudha Sarangi <anirudh@...inx.com>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v5] dma: Add Xilinx AXI Direct Memory Access Engine
 driver support

Hi Josh,

        Thanks for reviewing the patch

> -----Original Message-----
> From: Josh Cartwright [mailto:joshc@...com]
> Sent: Tuesday, March 03, 2015 12:12 AM
> To: Appana Durga Kedareswara Rao
> Cc: dan.j.williams@...el.com; vinod.koul@...el.com; Michal Simek; Soren
> Brinkmann; Srikanth Vemula; linux-kernel@...r.kernel.org; Srikanth
> Thokala; Anirudha Sarangi; dmaengine@...r.kernel.org; Appana Durga
> Kedareswara Rao; linux-arm-kernel@...ts.infradead.org
> Subject: Re: [PATCH v5] dma: Add Xilinx AXI Direct Memory Access Engine
> driver support
>
> Hello!
>
> I looked through your driver and have some comments.
>
> On Mon, Mar 02, 2015 at 11:25:11PM +0530, Kedareswara rao Appana wrote:
> > This is the driver for the AXI Direct Memory Access (AXI DMA) core,
> > which is a soft Xilinx IP core that provides high- bandwidth direct
> > memory access between memory and AXI4-Stream type target
> peripherals.
> >
> > Signed-off-by: Srikanth Thokala <sthokal@...inx.com>
> > Signed-off-by: Kedareswara rao Appana <appanad@...inx.com>
> [..]
> > +++ b/drivers/dma/Kconfig
> > @@ -425,6 +425,19 @@ config IMG_MDC_DMA
> >     help
> >       Enable support for the IMG multi-threaded DMA controller (MDC).
> >
> > +config XILINX_DMA
> > +   tristate "Xilinx AXI DMA Engine"
> > +   depends on (ARCH_ZYNQ || MICROBLAZE)
>
> Why do you need this dependency?  I'm assuming this IP has usefulness
> outside of microblaze and Zynq.
>
> > +   select DMA_ENGINE
> > +   help
> > +     Enable support for Xilinx AXI DMA Soft IP.
> > +
> > +   This engine provides high-bandwidth direct memory access
> > +   between memory and AXI4-Stream type target peripherals.
> > +   It has two stream interfaces/channels, Memory Mapped to
> > +   Stream (MM2S) and Stream to Memory Mapped (S2MM) for the
> > +   data transfers.
>
> Odd indention here.  At least indent this paragraph like the sentence above.

Ok Will do.

>
> [..]
> > +++ b/drivers/dma/xilinx/xilinx_dma.c
> [..]
> > +/**
> > + * xilinx_dma_halt - Halt DMA channel
> > + * @chan: Driver specific DMA channel  */ static void
> > +xilinx_dma_halt(struct xilinx_dma_chan *chan) {
> > +   int loop = XILINX_DMA_LOOP_COUNT;
> > +
> > +   dma_ctrl_clr(chan, XILINX_DMA_REG_CONTROL,
> > +                XILINX_DMA_CR_RUNSTOP_MASK);
> > +
> > +   /* Wait for the hardware to halt */
> > +   do {
> > +           if (dma_ctrl_read(chan, XILINX_DMA_REG_STATUS) &
> > +                   XILINX_DMA_SR_HALTED_MASK)
> > +                   break;
> > +   } while (loop--);
> > +
> > +   if (!loop) {
>
> Looks like a very subtle off-by-one error here.  (And elsewhere you use this
> pattern).
>

Ok Will do this change in the next version of the patch.

Regards,
Kedar.

>   Josh


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