[U-Boot] [RFC PATCH 0/3] Implement "fastboot flash" for eMMC

[Rob Herring]

On Wed, Jun 25, 2014 at 7:16 PM, Steve Rae <srae at broadcom.com> wrote:
> Rob,
>
>
> On 14-06-25 06:59 AM, Rob Herring wrote:
>>
>> On Mon, Jun 23, 2014 at 1:37 PM, Steve Rae <srae at broadcom.com> wrote:
>>>
>>> Rob & Sebastian
>>>
>>> I would appreciate your comments on this issue; I suspect that you had
>>> some
>>> ideas regarding the implementation of the fastboot "flash" and "erase"
>>> commands....
>>
>>
>> I agree with Lukasz's and Marek's comments unless there are good
>> reasons not to use it which can't be fixed. Curiously, USB mass
>> storage does not use the DFU backend, but I don't know why. Perhaps
>> there are incompatibilities or converting it is on the todo list. Are
>> your performance concerns measurable or it's just the fact you are
>> adding another layer?
>
>
> The concern is not performance related -- just the amount of (overhead) code
> required to implement the "DFU backend" versus calling
> mmc_dev->block_write()
>    (maybe someone can tell me where to interface into DFU: is it at
> "dfu_write() or ????)

Yes, I believe it is dfu_write.

>> I'd really like to see the eMMC backend be a generic block device
>> backend. There's no good reason for it to be eMMC/SD specific.
>
>
> As I understand it, the "block_write" callback function is in the
> "block_dev_desc_t". Isn't this the part of the "generic block device"
> interface? Please explain...

There are commands for SATA, SCSI (also SATA), eMMC, IDE, etc. They
are all pretty much the same set of sub-commands and duplicate the
same functionality. Those could all be combined to a single
implementation and/or command for block devices. That part is not DFU
related, but this problem then proliferates to other areas as it has
for DFU. The file drivers/dfu/dfu_mmc.c is mostly generic, but has
some eMMC dependencies with find_mmc_device and mmc_switch_part. So
read and write are already pretty much generic, but there's still some
work to do around device addressing/selection.

Rob