[U-Boot] [U-BOOT] [PATCH] mmc: enable switch partition function

[Wolfgang Denk]

Dear Lei Wen,

In message <AANLkTikdUN37v6tvYpy0hyJrB9OJ4XK-LyNPSida7Dyf at mail.gmail.com> you wrote:
> 
> EMMC is sightly different witht the other device with partition. 

Maybe.  But does this really require a different iunterface in the
U-Boot context?   I doubt that.

> For IDE as example, we could copy file between part A and B without problem.

No, we cannot. U-Boot can only read _or_ write form mass storage
operations, so a copy operation would always require a "read from
device to RAM buffer", "write to device from RAM buffer" sequence.
The same can obviously be done with EMMC as well.

> But for EMMC, the boot partition is different with the normal partition.
> We need to send a special command to do the switch, not with the
> different offset.

Thisis an internal implementation detail.  As a user, I do not want to
know about it. I just want to read or write data to some partition.
The rest is driver internals.

> If we need to copy file between those two partition, we need to send
> switch command
> before copy operation.

So where is the problem?  See above. We always have TWO separate
operations, and each of them will select a device/partition.

> It is a hardware one. IDE or usb masstorage has no such ability...

I see no difference from the user point of view.  The internal
implementation may be different, but that doesn't matter.

> For mmc may change the hardware partition, but fat command cannot...
> It is because
> it need to be compatiable with other devices that have no hardware partition...

I don;t understand what you want to tell me here.  My complaint is
that your new code is _not_ compatible with other divices, and I see
no reason for such an incompatibility.

Best regards,

Wolfgang Denk

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