linux-kernel - Re: [PATCH 1/3] ata: sata_dwc_460ex: use "dmas" DT property to find dma channel

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Message-ID: <yw1xa8p47h3w.fsf@unicorn.mansr.com>
Date:	Mon, 21 Dec 2015 00:58:11 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Julian Margetson <runaway@...dw.ms>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Tejun Heo <tj@...nel.org>, linux-ide@...r.kernel.org,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] ata: sata_dwc_460ex: use "dmas" DT property to find dma channel

Andy Shevchenko <andy.shevchenko@...il.com> writes:

> On Sun, Dec 20, 2015 at 8:49 PM, Måns Rullgård <mans@...sr.com> wrote:
>> Julian Margetson <runaway@...dw.ms> writes:
>>> On 12/20/2015 1:11 PM, Måns Rullgård wrote:
>>>> Julian Margetson <runaway@...dw.ms> writes:
>
>>> [   48.769671] ata3.00: failed command: READ FPDMA QUEUED
>>
>> Well, that didn't help.  I still think it's part of the problem, but
>> something else must be wrong as well.  The various Master Select fields
>> look like a good place to start.
>
> Master number (which is here would be either 1 or 0) should not affect
> as long as they are connected to the same AHB bus (I would be
> surprised if they are not).

I think they are not.  The relevant part of the block diagram for the
460EX looks something like this:

      +-----+
      | CPU |
      +-----+
         |
 +---------------+
 |      BUS      |
 +---------------+
    |         |
 +-----+   +-----+ 
 | DMA |   | RAM |
 +-----+   +-----+
    |
 +------+
 | SATA |
 +------+

The DMA-SATA link is private and ignores the address, which is the only
reason the driver can possibly work (it's programming a CPU virtual
address there).

>> Also, the manual says the LLP_SRC_EN
>> and LLP_DST_EN flags should be cleared on the last in a chain of blocks.
>> The old sata_dwc driver does this whereas dw_dma does not.
>
> Easy to fix, however I can't get how it might affect.

>From the Atmel doc:

  In Table 17-1 on page 185, all other combinations of LLPx.LOC = 0,
  CTLx.LLP_S_EN, CFGx.RELOAD_SR, CTLx.LLP_D_EN, and CFGx.RELOAD_DS are
  illegal, and causes indeterminate or erroneous behavior.

Most likely nothing happens, but I think it ought to be fixed.  In fact,
I have a patch already.

Come to think of it, I have an AVR32 dev somewhere.  Maybe I should dust
it off.

-- 
Måns Rullgård
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