linux-kernel - Re: Wrong "nollp" DW DMAC parameter value on ARC SDP.

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Message-ID: <1471264912.4887.117.camel@linux.intel.com>
Date:	Mon, 15 Aug 2016 15:41:52 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
Cc:	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
	"Nelson.Pereira@...opsys.com" <Nelson.Pereira@...opsys.com>,
	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>
Subject: Re: Wrong "nollp" DW DMAC parameter value on ARC SDP.

On Mon, 2016-08-15 at 11:10 +0000, Eugeniy Paltsev wrote:
> On Fri, 2016-08-12 at 17:08 +0300, Andy Shevchenko wrote:
> >  
> > > > > "nollp" parameter defines if DW DMAC channel supports multi
> > > > > block
> > > > > transfer or not.
> > > > >  
> > > > > It is calculated in runtime, but differently depending on on
> > > > > availability of pdata. If pdata is absent "nollp" is
> > > > > calculated
> > > > > using
> > > > > autoconfig hardware registers. Otherwise "nollp" is calculated
> > > > > using
> > > > > the next code construction:
> > > > > channel_writel(dwc, LLP, DWC_LLP_LOC(0xffffffff));
> > > > > dwc->nollp = DWC_LLP_LOC(channel_readl(dwc, LLP)) == 0;
> > > > > channel_writel(dwc, LLP, 0);
> > > > >  
> > > > > I realized that these methods give different results.
> > > > > For example on ARC AXS101 SDP in case of using autoconfig
> > > > > "nollp"
> > > > > was
> > > > > calculated as "true" (and DMAC works fine), 
> > > > > otherwise "nollp" was calculated as "false" (and DMAC doesn't
> > > > > work).
> > > > Can you show out what the value you read back?
> > > channel_readl(dwc, LLP) return 0xfffffffc
> > Nice.
> >  
> > Oh, forgot to ask, what are the DW_PARAMS and DWC_PARAMS[x] are on
> > the same hardware?
> DW_PARAMS: 0x38280b0c

Wow, you have two masters with number 3 and 4? (Just out of curiosity)

> DWC_PARAMS[0]: 0x4926d300
> DWC_PARAMS[1]: 0x4926d300
> DWC_PARAMS[2]: 0x4926d300
> DWC_PARAMS[3]: 0x4926d300

A-ha, seems you have CHx_HC_LLP == 0. That may explain.
 
> > > > > So I'm wondering how the code in question really works?
> > > > > From DW AHB DMAC databook I wasn't able to find anything
> > > > > relevant
> > > > > to
> > > > > this tricky implementation. Could you please clarify a little
> > > > > but
> > > > > what
> > > > > happens here?
> > > > "Table 4-1:
> > > > ...
> > > > Hardcode Channel x LLP register to 0?
> > > > ...
> > > > Description: If set to 1, hardcodes channel x Linked List
> > > > Pointer
> > > > register to 0 (LLPx.LOC == 0), ..."
> > So, any comment on this one? I suppose you may have an access to
> > some
> > internal Synopsys documentation which might shed a light. Or maybe I
> > missed something else which should be considered.
> Looks like this code based on idea, what if DMA ip-core doesn't have 
> LLP support it will not have LLP registers. It is not necessarily
> true.

Yep.

Consider to review 
http://www.spinics.net/lists/dmaengine/msg10682.html


> >  
> Please add this code to read "is_memcpy" and "is_nollp" property 
> from device tree.
> ----------------------------->8------------------------------
> diff --git a/drivers/dma/dw/platform.c b/drivers/dma/dw/platform.c
> index 5bda0eb..2712602 100644
> --- a/drivers/dma/dw/platform.c
> +++ b/drivers/dma/dw/platform.c
> @@ -129,6 +129,12 @@ dw_dma_parse_dt(struct platform_device *pdev)
>         if (of_property_read_bool(np, "is_private"))
>                 pdata->is_private = true;
>  
> +       if (of_property_read_bool(np, "is_memcpy"))
> +               pdata->is_memcpy = true;
> +
> +       if (of_property_read_bool(np, "is_nollp"))
> +               pdata->is_nollp = true;
> +
>         if (!of_property_read_u32(np, "chan_allocation_order", &tmp))
>                 pdata->chan_allocation_order = (unsigned char)tmp;

Please, make this as a patch and submit either separately, or with your
series mentioning that it has a dependency to my 8250 LPSS series.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy