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

[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.

>
>> >[..]
>> >
>> >Best regards,
>> >Marek Vasut
>
>Best regards,
>Marek Vasut