[PATCH 02/13] arm: imx: Remove unused CONFIG_xxx_TAG support

[Tom Rini]

On Thu, Feb 04, 2021 at 06:56:47AM -0300, Fabio Estevam wrote:
> Hi Tom,
> 
> [Adding Bryan]
> 
> On Thu, Feb 4, 2021 at 12:49 AM Tom Rini <trini at konsulko.com> wrote:
> 
> > CONFIG_SERIAL_TAG is only used to configure the ATAG serial record.  It
> > does nothing else.  On i.MX8* this is already being discarded.  On i.MX7
> > we see things like:
> >             warp7          : all -144 rodata +32 text -176
> >                u-boot: add: 0/-2, grow: 0/-2 bytes: 0/-160 (-160)
> >                  function                                   old     new   delta
> >                  params                                       4       -      -4
> >                  get_board_serial                            20       -     -20
> >                  board_late_init                             96      56     -40
> >                  boot_prep_linux                            156      60     -96
> 
> But then it will remove the support of reading serial number via fuses
> which was added by:
> 
> commit 852cc548b3fdf6d5b46e2a96f876d14608ccdcf4
> Author: Bryan O'Donoghue <bryan.odonoghue at linaro.org>
> Date:   Mon Mar 26 15:27:34 2018 +0100
> 
>     warp7: Set u-boot serial# based on OTP value
> 
>     u-boot has a standard "serial#" environment variable that is suitable
>     for storing the iSerial number we will supply via the USB device
>     descriptor. serial# is automatically picked up by the disk subsystem in
>     u-boot - thus providing a handy unique identifier in /dev/disk/by-id as
>     detailed below.
> 
>     Storing the hardware serial identifier in serial# means we can change the
>     serial# if we want before USB enumeration - thus making iSerial automatic
>     via OTP but overridable if necessary.
> 
>     This patch reads the defined OTP fuse and sets environment variable
>     "serial#" to the value read.
> 
>     With this patch in place the USB mass storage device will appear in
>     /dev/disk/by-id with a unique name based on the OTP value. For example
> 
>     /dev/disk/by-id/usb-Linux_UMS_disk_0_WaRP7-0xf42400d3000001d4-0:0
> 
>     Signed-off-by: Bryan O'Donoghue <bryan.odonoghue at linaro.org>
>     Cc: Fabio Estevam <fabio.estevam at nxp.com>
>     Cc: Rui Miguel Silva <rui.silva at linaro.org>
>     Cc: Ryan Harkin <ryan.harkin at linaro.org>
>     Reviewed-by: Fabio Estevam <fabio.estevam at nxp.com>

I did miss that one.  I'm not sure if that's abusing a symbol or clever
use of the symbol.  I will have to v2 this one then.

> > Currently, yes.  Historically ever?  Or even if so, you're OK just removing all
> > of that code as well?  Thanks.
> 
> mx5 and mx6 used to boot board files in the past (NXP kernel 2.6.35
> for mx5 or 3.0.x for mx6).
> 
> Such kernels are not even maintained by the NXP, so we should not
> worry about booting non-DT with i.MX.

So you're OK with removing ATAGs support from i.MX5/6 from mainline?
But there's the unresolved question of the best way to populate
"serial#".  Yes?  Thanks.

-- 
Tom
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