linux-kernel - Re: [PATCH v2] dmaengine: vdma: Add 64 bit addressing support to the driver

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Date:	Mon, 21 Mar 2016 18:17:48 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Michal Simek <michals@...inx.com>,
	Soren Brinkmann <sorenb@...inx.com>,
	Dan Williams <dan.j.williams@...el.com>,
	"afaerber@...e.de" <afaerber@...e.de>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Appana Durga Kedareswara Rao <appanad@...inx.com>,
	Anirudha Sarangi <anirudh@...inx.com>,
	Srikanth Vemula <svemula@...inx.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>
Subject: Re: [PATCH v2] dmaengine: vdma: Add 64 bit addressing support to the driver

Hi Anurag,

On Wednesday 23 Sep 2015 15:12:36 Anurag Kumar Vulisha wrote:
> On Monday, September 21, 2015 9:27 PM Vinod Koul wrote:
> > On Thu, Aug 27, 2015 at 09:19:18PM +0530, Anurag Kumar Vulisha wrote:
> >> This VDMA  is a soft ip, which can be programmed to support
> >> 32 bit addressing or greater than 32 bit addressing.
> >> 
> >> When the VDMA ip is configured for 32 bit address space the transfer
> >> start address is specified by a single register.
> > 
> > would be good to specfiy which one
> 
> Will change  this in v3

What happened to v3 ? :-)

> >> When the  VDMA core is configured for an address space greater than 32
> >> then each start address is specified by a combination of two
> >> registers. The first register specifies the LSB 32 bits of address,
> >> while the next register specifies the MSB 32 bits of address.For
> >> example,5Ch will specify the LSB 32 bits while 60h will specify the
> >> MSB 32 bits of the first start address.So we need to program two
> >> registers at a time.
> > 
> > can we have spaces after full stops and commas!
> 
> Will take care of this in v3 patch.
> 
> >> +/* Since vdma driver is trying to write to a register offset which is
> >> +not a
> >> + * multiple of 64 bits(ex : 0x5c), we are writing as two separate 32
> >> +bits
> >> + * instead of a single 64 bit register write.
> >> + */
> > 
> > This is not kernel style for multi-lines, pls refer to
> > Documentation/CodingStyle
> 
> Will address this in v3 patch
> 
> >> +
> >> +static inline void vdma_desc_write_64(struct xilinx_vdma_chan *chan,
> >> u32 reg,
> >> +                            u32 value_lsb, u32 value_msb)
> >> +{
> >> +   /* Write the lsb 32 bits*/
> >> +   writel(value_lsb, chan->xdev->regs + chan->desc_offset + reg);
> >> +
> >> +   /* Write the msb 32 bits */
> >> +   writel(value_msb, chan->xdev->regs + chan->desc_offset + reg + 4);
> > 
> > why not writeq
> 
> We are trying to write at a register address(ex:0x5c) which is not aligned
> on 8 bytes  boundary.So if I try to use 64 bit write on it,unalignment 
> fault is getting  generated.To avoid that we are using two separate 32  bit
> writes. We had this discussion in previous versions of this patch with
> Laurent Pinchart .I have also added this exaplanation in the comments above
> this function.
>
> >> +   err = of_property_read_u32(node, "xlnx,addrwidth", &addr_width);
> >> +
> >> +   if (err < 0) {
> >> +           /* Setting addr_width property to default 32 bits */
> >> +           addr_width = 32;
> >> +   }
> > 
> > braces for a single line statement! Also space is redandant before if
> > condition
>
> Will take care of this in v3 patch

-- 
Regards,

Laurent Pinchart