[U-Boot] KARO TX25: Fix NAND Flash R/W cycle times

The NAND Flash of the KARO TX25 board is a Samsung K9F1G08U0B with 25-ns R/W
cycle times. However, the NFC clock for this board was set to 66.5 MHz, so using
the NFC driver in symmetric mode (i.e. 1 NFC clock cycle = 1 NF R/W cycle)
resulted in NF R/W cycle times of 15 ns, hence corrupted NF accesses.

This patch fixes this issue by setting the NFC clock to the highest frequency
complying to the 25-ns NF R/W cycle times specification, i.e. 33.25 MHz.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: John Rigby <jcrigby@gmail.com>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Daniel Gachet <Daniel.Gachet@hefr.ch>
---
This patch is a replacement solution that I suggest instead of
http://patchwork.ozlabs.org/patch/174735/ since there is no need for a
CONFIG_SYS_NAND_MXC_NFC_TWO_CYCLES config option in the NFC driver.

It still has to be tested by someone having this board, but I'm very confident
that it works since I have another PCB design based on the i.MX25 with a NAND
Flash with the same timings that works fine using these clock settings.

 .../board/karo/tx25/lowlevel_init.S                |    8 ++++++++
 1 file changed, 8 insertions(+)

On 08/08/2012 15:55, Benoît Thébaudeau wrote:
> The NAND Flash of the KARO TX25 board is a Samsung K9F1G08U0B with 25-ns R/W
> cycle times. However, the NFC clock for this board was set to 66.5 MHz, so using
> the NFC driver in symmetric mode (i.e. 1 NFC clock cycle = 1 NF R/W cycle)
> resulted in NF R/W cycle times of 15 ns, hence corrupted NF accesses.
> 
> This patch fixes this issue by setting the NFC clock to the highest frequency
> complying to the 25-ns NF R/W cycle times specification, i.e. 33.25 MHz.
> 
> Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
> Cc: John Rigby <jcrigby@gmail.com>
> Cc: Scott Wood <scottwood@freescale.com>
> Cc: Stefano Babic <sbabic@denx.de>
> Cc: Daniel Gachet <Daniel.Gachet@hefr.ch>
> ---
> This patch is a replacement solution that I suggest instead of
> http://patchwork.ozlabs.org/patch/174735/ since there is no need for a
> CONFIG_SYS_NAND_MXC_NFC_TWO_CYCLES config option in the NFC driver.
> 
> It still has to be tested by someone having this board, but I'm very confident
> that it works since I have another PCB design based on the i.MX25 with a NAND
> Flash with the same timings that works fine using these clock settings.
> 
>  .../board/karo/tx25/lowlevel_init.S                |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git u-boot-2012.07.orig/board/karo/tx25/lowlevel_init.S u-boot-2012.07/board/karo/tx25/lowlevel_init.S
> index 823df10..eb3f187 100644
> --- u-boot-2012.07.orig/board/karo/tx25/lowlevel_init.S
> +++ u-boot-2012.07/board/karo/tx25/lowlevel_init.S
> @@ -67,6 +67,14 @@
>  	write32	0x53f80008, 0x20034000
>  
>  	/*
> +	 * PCDR2: NFC = 33.25 MHz
> +	 * This is required for the NAND Flash of this board, which is a Samsung
> +	 * K9F1G08U0B with 25-ns R/W cycle times, in order to make it work with
> +	 * the NFC driver in symmetric (i.e. one-cycle) mode.
> +	 */
> +	write32	0x53f80020, 0x01010103
> +
> +	/*

This is a very local change, only for the Karo-TX25. I see no problem
with it.

Acked-by: Stefano Babic <sbabic@denx.de>

Best regards,
Stefano Babic

On 08/08/2012 15:55, Benoît Thébaudeau wrote:
> The NAND Flash of the KARO TX25 board is a Samsung K9F1G08U0B with 25-ns R/W
> cycle times. However, the NFC clock for this board was set to 66.5 MHz, so using
> the NFC driver in symmetric mode (i.e. 1 NFC clock cycle = 1 NF R/W cycle)
> resulted in NF R/W cycle times of 15 ns, hence corrupted NF accesses.
> 
> This patch fixes this issue by setting the NFC clock to the highest frequency
> complying to the 25-ns NF R/W cycle times specification, i.e. 33.25 MHz.
> 

Applied to u-boot-imx(fix), thanks.

Best regards,
Stefano Babic