linux-kernel - Re: [PATCH] MTD: LPC32xx SLC NAND driver

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Date:	Tue, 15 May 2012 15:20:55 +0200
From:	Roland Stigge <stigge@...com.de>
To:	Huang Shijie <b32955@...escale.com>
CC:	dedekind1@...il.com, Bastian Hecht <hechtb@...glemail.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Lei Wen <leiwen@...vell.com>, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org, dwmw2@...radead.org,
	kevin.wells@....com, srinivas.bakki@....com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] MTD: LPC32xx SLC NAND driver

Hi Artem and Huang,

thank you for your feedback!

On 05/15/2012 10:15 AM, Huang Shijie wrote:
>> On Sat, 2012-05-12 at 15:29 +0200, Roland Stigge wrote:
>>> +       /*
>>> +        * The DMA is finished, but the NAND controller may still have
>>> +        * buffered data. Wait until all the data is sent.
> When all the data is sent, is there an interrupt for this?

Bad news is: No

Good news is: The previous DMA operation finished with an interrupt
which according to the manual should already corresponds to this
condition. Tests show that at this point of sampling:

>>> +       timeout = LPC32XX_DMA_SIMPLE_TIMEOUT;
>>> +       while ((readl(SLC_STAT(host->io_base))&  SLCSTAT_DMA_FIFO)
>>> +&&  (timeout>  0))
>>> +               timeout--;

... the condition is always true and always just jumps over this loop,
at least with my hardware.

>> /* Chip reaction time timeout in milliseconds */
>> #define LPC32XX_DMA_TIMEOUT 100
>>
>> timeout = loops_per_jiffy * msecs_to_jiffies(LPC32XX_DMA_TIMEOUT);
>>
>> while ((readl(...))&&  timeout-->  0)
>>     cpu_relax();

As I understand loops_per_jiffy, this loop will take much longer than
the 100 ms you defined above?

Anyway, I will keep the loop for safety reasons, add an msleep() and add
a warning, should the loop be entered _at all_.

Maybe someone from NXP can give us more insight here? Maybe the
condition check isn't necessary anymore after I ported the driver to
dmaengine (this controller is always wired together with an amba-pl080
in the LPC32xx)?

Thanks in advance,

Roland
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