[U-Boot] [PATCH 1/2] doc: README.fuse: Add an example on how to use the fuse API on mx6q

[Benoît Thébaudeau]

Hi Fabio,

On Tuesday, December 17, 2013 9:03:40 PM, Fabio Estevam wrote:
> From: Fabio Estevam <fabio.estevam at freescale.com>
> 
> When using the fuse API in U-boot user must calculate the 'bank' and 'word'
> values.
> 
> Provide a real example on how to calculate such values for the mx6q.
> 
> Signed-off-by: Fabio Estevam <fabio.estevam at freescale.com>
> ---
>  doc/README.fuse | 57
>  +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 57 insertions(+)
> 
> diff --git a/doc/README.fuse b/doc/README.fuse
> index 1bc91c4..aca1e5e 100644
> --- a/doc/README.fuse
> +++ b/doc/README.fuse
> @@ -65,3 +65,60 @@ Configuration:
>  
>     CONFIG_CMD_FUSE
>        Define this to enable the fuse commands.
> +
> +Example:
> +
> +For reading the MAC address fuses on a MX6Q:
> +
> +- The MAC address are stored in two fuse addresses (the fuse addresses are
> +described in the Fusemap Descriptions table from the mx6q Reference Manual):
> +
> +0x620[31:0] - MAC_ADDR[31:0]
> +0x630[15:0] - MAC_ADDR[47:32]
> +
> +In order to use the fuse API, we need to pass the bank and word values,
> which
> +are calculated as below:
> +
> +Fuse address for the lower MAC address: 0x620
> +Base address for the fuses: 0x400
> +
> +(0x620 - 0x400)/0x10 = 0x22 = 34 decimal
> +
> +As the fuses are arranged in banks of 8 words:
> +
> +34 / 8 = 4 and the remainder is 2, so in this case:
> +
> +bank = 4
> +word = 2
> +
> +And the U-boot command would be:
> +
> +=> fuse read 4 2
> +Reading bank 4:
> +
> +Word 0x00000002: 9f027772
> +
> +Doing the same for the upper MAC address:
> +
> +Fuse address for the upper MAC address: 0x630
> +Base address for the fuses: 0x400
> +
> +(0x630 - 0x400)/0x10 = 0x23 = 35 decimal
> +
> +As the fuses are arranged in banks of 8 words:
> +
> +35 / 8 = 4 and the remainder is 3, so in this case:
> +
> +bank = 4
> +word = 3
> +
> +And the U-boot command would be:
> +
> +=> fuse read 4 3
> +Reading bank 4:
> +
> +Word 0x00000003: 00000004
> +
> +,which matches the ethaddr value:
> +=> echo ${ethaddr}
> +00:04:9f:02:77:72
> --
> 1.8.1.2

Note that the documentation in this file is also completed for i.MX6 by
doc/README.mxc_ocotp and doc/README.imx6, as explained in each README. The
information that you add here regarding the location of the MAC fuses for i.MX6Q
is already present in doc/README.imx6.

Regarding the 'calculation' part, it is actually not needed since the values
obtained with these calculations are already given by the reference manual in
'46.5 OCOTP Memory Map/Register Definition'.

Examples could still be interesting though. What do you think?
 - Should the calculation part be removed and replaced with a reference to the
   RM §46.5 be added?
 - Should this example be moved to doc/README.imx6, or kept in doc/README.fuse
   as a generic example for the fuse API?
 - Should an example be added to show how to read the whole MAC address with a
   single fuse command (i.e. 'fuse read 4 2 2')?

Best regards,
Benoît