[U-Boot] Reg. CFI flash_init and hardware write protected devices

[Frank Svendsbøe]

On Wed, Jun 1, 2011 at 6:59 PM, Frank Svendsbøe
<frank.svendsboe at gmail.com> wrote:
> On Wed, Jun 1, 2011 at 5:34 PM, Stefan Roese <sr at denx.de> wrote:
>> Hi Frank,
>>
>> On Wednesday 01 June 2011 16:33:14 Frank Svendsbøe wrote:
>>> >> Simply because disabling write-protection is not impossible after
>>> >> installation. Our device will be located 3000m below sea level.
>>> >
>>> > I see.
>>>
>>> Hmm.. then you read my mind :) I meant to say "is not possible" and not "is
>>> not impossible" :)
>>
>> Yep. I read so fast, that I didn't catch the misspelled words. ;)
>>
>>> Thanks, this worked for me. Is it ok for you too?
>>>
>>> diff --git a/drivers/mtd/cfi_flash.c b/drivers/mtd/cfi_flash.c
>>> index 6039e1f..99360af 100644
>>> --- a/drivers/mtd/cfi_flash.c
>>> +++ b/drivers/mtd/cfi_flash.c
>>> @@ -176,6 +176,7 @@ u64 flash_read64(void *addr)__attribute__((weak,
>>> alias("__flash_read64")));
>>>  #define flash_read64 __flash_read64
>>>  #endif
>>>
>>> +
>>
>> Don't add this empty line.
>>
>
> Thanks for spotting this. I'll remove this of course.
>
>>>  /*-----------------------------------------------------------------------
>>>   */
>>>  #if defined(CONFIG_ENV_IS_IN_FLASH) ||
>>> defined(CONFIG_ENV_ADDR_REDUND) || (CONFIG_SYS_MONITOR_BASE >=
>>> CONFIG_SYS_FLASH_BASE)
>>> @@ -2151,7 +2152,8 @@ void flash_protect_default(void)
>>>  #endif
>>>  }
>>>
>>> -unsigned long flash_init (void)
>>> +unsigned long flash_init(void) __attribute__((weak,
>>> alias("__flash_init"))); +unsigned long __flash_init (void)
>>>  {
>>>       unsigned long size = 0;
>>>       int i;
>>
>> Looks good. I have no objections. Please go ahead and send this as a "proper"
>> patch.
>>
>
> Will do (as soon as I get back to work).
>
> Best regards,
> Frank.
>

Hi Stefan,
A few weeks ago, I applied this change and everything worked fine in
U-Boot. However, I didn't succeed doing the same hack in Linux. I've
done some hardcoding experiments in drivers/mtd/chips/cfi_probe.c, but
so far no success. After reading some CFI manuals, it seems CFI
will/should use bus write operations even during CFI read operations.
Can you confirm this? Then my next question is how come U-Boot read
operations works by just hardcoding the flash geometry. It seems
U-Boot utilize just plain localbus accesses to read flash data, ie.
not the "CFI protocol". What did I miss here.. ?

Now I'm considering two options: 1) Either write a custom flash map
driver, and access the flash the same way U-Boot does, or 2) try to
convince the FPGA designers that our way of forcing write protection
is not according the the CFI specifications, and should be done
otherwise. What do you think is the best solution?

Is there anybody else out there supporting hardware write protection
on CFI devices?

Best regards,
Frank