linux-kernel - Re: [PATCH 08/11] spi-dw: Ensure fifo lenght is set.

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Message-ID: <4E02AC85.90300@gmail.com>
Date:	Wed, 22 Jun 2011 20:01:25 -0700
From:	Dirk Brandewie <dirk.brandewie@...il.com>
To:	Feng Tang <feng.tang@...el.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"spi-devel-general@...ts.sourceforge.net" 
	<spi-devel-general@...ts.sourceforge.net>
Subject: Re: [PATCH 08/11] spi-dw: Ensure fifo lenght is set.

On 06/22/2011 07:41 PM, Feng Tang wrote:
>
>
> On Thu, 23 Jun 2011 10:00:10 +0800
> "dirk.brandewie@...il.com"<dirk.brandewie@...il.com>  wrote:
>
>> From: Dirk Brandewie<dirk.brandewie@...il.com>
>>
>> Bug on fifo_len not being set.  The fifo sizing routine does not work
>> since the txfltr register can not be written while the controller is
>> enabled. The max value of txfltr can be larger than the fifo.  The
>> register allows values upto 0x3f (63) the fifo depth on the Intel
>> SOC's if 40
>>
>> Signed-off-by: Dirk Brandewie<dirk.brandewie@...il.com>
>> ---
>>   drivers/spi/spi-dw.c |   18 ++----------------
>>   1 files changed, 2 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
>> index ad92826..cc38aa0 100644
>> --- a/drivers/spi/spi-dw.c
>> +++ b/drivers/spi/spi-dw.c
>> @@ -776,25 +776,11 @@ static int destroy_queue(struct spi_dw *dws)
>>   /* Restart the controller, disable all interrupts, clean rx fifo */
>>   static void spi_dw_hw_init(struct spi_dw *dws)
>>   {
>> +	BUG_ON(!dws->fifo_len);
>> +
>>   	spi_dw_disable(dws);
>>   	spi_dw_mask_intr(dws, 0xff);
>>   	spi_dw_enable(dws);
>> -
>> -	/*
>> -	 * Try to detect the FIFO depth if not set by interface
>> driver,
>> -	 * the depth could be from 2 to 256 from HW spec
>> -	 */
>> -	if (!dws->fifo_len) {
>> -		u32 fifo;
>> -		for (fifo = 2; fifo<= 257; fifo++) {
>> -			dw_writew(dws, txfltr, fifo);
>> -			if (fifo != dw_readw(dws, txfltr))
>> -				break;
>> -		}
>> -
>> -		dws->fifo_len = (fifo == 257) ? 0 : fifo;
>> -		dw_writew(dws, txfltr, 0);
>> -	}
>>   }
>
> This code is requested by other community developers, the FIFO
> length is adjustable for the dw_spi core when deployed on
> different platforms, for those who are not certain about the
> FIFO len, they can use this code to probe the FIFO len.
>
> So we need to keep it.
>

Then I have bad documentation because document I have says that you can NOt 
write to txfltr while the controller is enabled.  The sizing routine as it 
stands can't work for the implementation in Moorsetown and Medfield.

If there are other SOC's that are implementing different semantics for txfltr we 
will need to handle this differently and do some runtime detection of how the 
fifo should be sized.

Can you give ne a reference to the person that requiested the sizing code so I 
can follow-up
>>
>>   int __devinit spi_dw_add_host(struct spi_dw *dws)

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