[U-Boot] [PATCH] mx6: Avoid writing to read-only bits in imximage.cfg

[Marek Vasut <marex@denx.de>]

Dear Liu Hui-R64343,

> Hi, Marek,
> 
> >-----Original Message-----
> >From: Marek Vasut [mailto:marex at denx.de]
> >Sent: Wednesday, June 13, 2012 8:25 PM
> >To: u-boot at lists.denx.de
> >Cc: Liu Hui-R64343; Dirk Behme
> >Subject: Re: [U-Boot] [PATCH] mx6: Avoid writing to read-only bits in
> >imximage.cfg
> >
> >Dear Liu Hui-R64343,
> >
> >[...]
> >
> >> >> >> According to REV C manual, the register IOMUXC_IOMUXC_GPR4 has
> >> >> >> bits
> >> >> >> 4 and 5 read-only and the value is always set as zero.
> >> >> >> So write '0' to these bits instead of writing '1'.
> >> >> >
> >> >> >Jason, Fabio: What do you think? You should be the datasheet
> >> >> >'masters' ;)
> >> >> 
> >> >> Yes, according to the RM,
> >> >> 5
> >> >> Reserved
> >> >> This read-only field is reserved and always has the value 0.
> >> >> 4
> >> >> Reserved
> >> >> This read-only field is reserved and always has the value 0.
> >> >> 
> >> >> So, write 1 should have no effect.
> >> >
> >> >I really dislike how "write 1 should have no effect" sounds. Can you
> >> >please check with HW people?
> >> 
> >> Since this is read-only bit, if you write 1 to it, it will have no
> >> effect.
> >
> >For how long do you work with hardware? Did it never occur to you that
> >when you wrote 1 to an "reserved" bit, it either did something you didn't
> >expect or you had to rework it later because the new CPU has that bit for
> >something else?
> >
> >> Yes, to avoid the confusion, for example to do the read-back check, I
> >> agree with not writing '1' to the read-only bit.
> >
> >Please, ask the hardware people about this.
> 
> Yes, I will and back to you.

Thanks!

btw. sorry, I didn't meant to offend you.

Best regards,
Marek Vasut