From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>,
"dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Nelson Pereira <Nelson.Pereira@synopsys.com>,
"viresh.kumar@linaro.org" <viresh.kumar@linaro.org>,
"vinod.koul@intel.com" <vinod.koul@intel.com>,
"linux-snps-arc@lists.infradead.org"
<linux-snps-arc@lists.infradead.org>
Subject: Re: Wrong "nollp" DW DMAC parameter value on ARC SDP.
Date: Fri, 12 Aug 2016 13:59:44 +0300 [thread overview]
Message-ID: <1470999584.4887.94.camel@linux.intel.com> (raw)
In-Reply-To: <1470988994.21247.33.camel@synopsys.com>
On Fri, 2016-08-12 at 08:03 +0000, Eugeniy Paltsev wrote:
> Hi,
>
> "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?
>
> 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), ..."
> Maybe we should add "nollp" field in pdata structure and receive it
> from pdata/device tree (like we use "is_private" or "is_memcpu"
> fields)
Yeah, perhaps we can remove that trick since we need this flag to be set
on Intel Quark which might have the same issue as your case [1].
[1] http://www.spinics.net/lists/linux-serial/msg22948.html
--
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy
next prev parent reply other threads:[~2016-08-12 10:59 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-12 8:03 Wrong "nollp" DW DMAC parameter value on ARC SDP Eugeniy Paltsev
2016-08-12 10:59 ` Andy Shevchenko [this message]
2016-08-12 13:36 ` Eugeniy Paltsev
2016-08-12 14:08 ` Andy Shevchenko
2016-08-15 11:10 ` Eugeniy Paltsev
2016-08-15 12:41 ` Andy Shevchenko
2016-08-16 11:32 ` Eugeniy Paltsev
2016-08-16 11:46 ` Andy Shevchenko
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