linux-kernel - Re: [PATCH v4 09/11] dmaengine: dw: Initialize min

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Message-ID: <20200529104119.qrqoptp5iz5hs56r@mobilestation>
Date:   Fri, 29 May 2020 13:41:19 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Vinod Koul <vkoul@...nel.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>, <linux-mips@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <dmaengine@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 09/11] dmaengine: dw: Initialize min_burst capability

On Fri, May 29, 2020 at 01:29:02PM +0300, Andy Shevchenko wrote:
> On Fri, May 29, 2020 at 01:25:15PM +0300, Andy Shevchenko wrote:
> > On Fri, May 29, 2020 at 01:23:59AM +0300, Serge Semin wrote:
> > > According to the DW APB DMAC data book the minimum burst transaction
> > > length is 1 and it's true for any version of the controller since
> > > isn't parametrised in the coreAssembler so can't be changed at the
> > > IP-core synthesis stage. Let's initialise the min_burst member of the
> > > DMA controller descriptor so the DMA clients could use it to properly
> > > optimize the DMA requests.
> 
> ...
> 
> > >  	/* DMA capabilities */
> > 
> > > +	dw->dma.min_burst = 1;
> > 
> > Perhaps then relaxed maximum, like
> > 
> > 	dw->dma.max_burst = 256;
> > 
> > (channels will update this)
> > 
> > ?
> 

> And forgot to mention that perhaps we need a definitions for both.

By "definitions for both" do you mean a macro with corresponding parameter
definition like it's done for the max burst length in the next patch?
Something like this:
--- include/linux/platform_data/dma-dw.h
+++ include/linux/platform_data/dma-dw.h
+#define DW_DMA_MIN_BURST	1
+#define DW_DMA_MAX_BURST	256

?

-Sergey

> 
> > >  	dw->dma.src_addr_widths = DW_DMA_BUSWIDTHS;
> > >  	dw->dma.dst_addr_widths = DW_DMA_BUSWIDTHS;
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>