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

[Lukasz Majewski]

Hi Rob,

> 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.

dfu_write should be used.

> 
> >> 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. 

dfu_mmc.c is intended to handle eMMC/SD card writing. Please note that
there are other files - dfu_nand.c and dfu_raw.c, which are responsible
for accessing and storing data to other medium.

The "generic" file here is the dfu.c which tries to combine all
available media.

> So
> read and write are already pretty much generic, but there's still some
> work to do around device addressing/selection.
> 
> Rob


-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group