[U-Boot] CFI Driver Problem: flash not ready

[Wolfgang Denk]

Dear Scott,

In message <48FBADA6.3090505 at psyent.com> you wrote:
> 
> > Why the heck does flash_is_busy() return 0 when the flashobviously is
> > still busy?
> 
> Does this use the toggle bit detection? I saw the same symptoms
> with Nios II. Basically, the memory controller was reading the
> 16-bit flash twice to obtain a full 32-bit word, then returning just
> the first 16-bits. So, I would never see the toggle bit changing.
> 
> Not sure if this is similar to your situation ... but it was a real
> pain-in-the-butt to finally understand what was happening in my
> situation.

My situation is indeed similar. The 64 bit read (which is supposed to
be implemented by flash_read64()) is in fact broken downinto  two  32
bit reads, with the consequence that flash_toggle() does not work any
more,  because  of  reading the *same* addresses twice we are reading
alternate addresses (addr, addr+4, addr, addr+4).

This patch fixes the problem for me:


diff --git a/drivers/mtd/cfi_flash.c b/drivers/mtd/cfi_flash.c
index c40bf66..24e9b9f 100644
--- a/drivers/mtd/cfi_flash.c
+++ b/drivers/mtd/cfi_flash.c
@@ -596,7 +596,8 @@ static int flash_toggle (flash_info_t * info, flash_sect_t sect,
 		retval = flash_read32(addr) != flash_read32(addr);
 		break;
 	case FLASH_CFI_64BIT:
-		retval = flash_read64(addr) != flash_read64(addr);
+		retval = ( (flash_read32( addr ) != flash_read32( addr )) ||
+			   (flash_read32(addr+4) != flash_read32(addr+4)) );
 		break;
 	default:
 		retval = 0;

However, I'm not really happy about  this.  Maybe  we  should  really
implement an atomic 64 bit read operation for flash_read64()? But the
only solution I could come up for this would be pretty complex:

	save MSR;
	set Floating Point enable bit in MSR;
	use "lfd" instruction to perform atomic 64 bit read;
	use "stfd" to store value to temporary variable on stack;
	load u64 from temporary variable;
	restore saved MSR;
	return u64 value;

Is this worth the trouble?

Is it valid to assume that a processor which has the flashon a 64 bit
bus will also have a FPU?

Would ne need to save/restore the FP register used here?

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Documentation is the castor oil of programming.
Managers know it must be good because the programmers hate it so much.