[U-Boot] [PATCH 01/11] DM: add block device core

[Marek Vasut]

Dear Pavel Herrmann,

> On Friday 21 of September 2012 17:34:27 Marek Vasut wrote:
> > Dear Pavel Herrmann,
> > 
> > [...]
> > 
> > > > > blockctrl = AHCI, PIIX... whichever chip you have between SATA and
> > > > > PCI (or generally disk-bus and board-bus)
> > > > 
> > > > So this is for sata ? Or will it also by used for SD/USB flash discs?
> > > 
> > > no, blockctrl will be used for SATA, PATA, SCSI, and anything of the
> > > sort (device with several ports, block devices on said ports, ability
> > > to send read/write/query commands to devices on ports - definitely not
> > > USB, possibly also SD, but you probably want more operations from SD)
> > 
> > Why not USB flash ? Why not SD, what other stuff do you need for that? Is
> > the API not misdesigned then?
> 
> you should have a blockdev driver for USB flash and SD, but not blockctrl

I'm lost again. Do I also need a blockdev driver for SATA controller now that I 
need a blockdev driver for SD card controller ?

> > > > > blockdev = disk, partition, SD card
> > > > 
> > > > Uh, let's say I understand (even if I don't see the correlation
> > > > between partition and SD card)
> > > 
> > > they are an ordered bunch of blocks with a "conventional" filesystem on
> > > them
> > 
> > You might want to do RAW reads, so why do you put filesystem into this
> > context?
> 
> yes, you can do raw reads, but in most cases you are using a filesystem.

Not true, see how env is stored to these media.

> i
> put filesystem there to differentiate from nand devices (which have a
> special flash- based filesystems in most cases).

Not true, raw IO on flash media is often used too.

> > > > > - something that does basic checks
> > > > > (range, possibility of operation) and submits operations to correct
> > > > > parent (blockctrl, MMC controller, whatnot).
> > > > 
> > > > Ascii art might help here greatly (how these pieces fall together). I
> > > > think I do understand it though.
> > > 
> > > current code
> > > user -> FS -> offset calculation from partition info -> drivers/disk
> > > 
> > > new code
> > > user -> FS -> blockdev -> blockctrl (or USB or SD controller)
> > 
> > So your "blockctrl" should do the USB/SD/whatever muxing.
> 
> no, blockdev shoud be the last common part, for SD/USB, you should have a
> different blockdev driver, that uses USB/SD API for the actual works
> 
> blockctrl is just an unified look at whatever now resides in drivers/block

Answer my question, you are contradicting yourself in your answer. So again, 
does "blockctrl" do the muxing between the downstream drivers (SD blockdev, USB 
blockdev, SATA blockdev, IDE blockdev ... ) ?

> > > partition blockdev does all the offset calculation and range check that
> > > FSs
> > > do now, and then submits the operation to the parent blockdev, which in
> > > turn submits it to blockctrl (or an SD controller in case of a SD card,
> > > or USB controller in case of a USB flash)
> > 
> > Make sure you document this in the next series.
> > 
> > > Pavel Herrmann
> > 
> > Best regards,
> > Marek Vasut

Best regards,
Marek Vasut