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

[Marek Vasut <marex@denx.de>]

Dear Pavel Herrmann,

[...]

> > > 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 ?
> 
> you need a blockdev for a blockctrl (see [5/11]), and you need a blockctrl
> driver for your SATA controller

So "blockctrl" == The controller driver? Viva abbrevs. Rename it to 
block_controller_driver .

> you can either implement your SD as a blockctrl and use that blockdev

SD as in ... SD card or SD host controller ? Use what blockdev ?

> , or
> implement a separate blockdev for your SD card (this is the original
> intention)

Ok, so the general abstration is to have a block_controller_driver (blockctrl in 
your parlance) for each and every driver in drivers/block _and_ which provides 
only basic read/write block for the downstream drivers (block_device) attached 
to it _and_ proxifies them for particular device type handlers?

Now block_device (blockdev) is either a whole disc, partition, or subpartition. 
It exports read/write block operations, but to complete them, it uses upcalls 
into it's parent, yes? These upcalls stop at first block_controller_driver, 
correct?

The user only ever uses the read/write block operations of the block_device, 
yes?

> I have not looked at current SD API, but i do recall seeing some non-memory
> SDIO cards (wifi for example, not sure u-boot supports this though), so i
> dont think SD should be implemented as a blockctrl

They are not. But you should have looked at them since if you don't, that means 
you ignored fundamental part of the block interface.

But anyway, in case of SD card, the upcalls stop at block_controller_driver, 
which handles the block IO the specific SD controller way?

> > > > > > > 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 ... ) ?
> 
> again, no
> 
> blockctrl is a common API primarily for SATA/PATA/SCSI controllers,
> blockdev is an abstraction of any block device, therefore you should have
> a AHCI blockctrl, piix blockctrl, bfin blockctrl, sil3114 blockctrl (add
> anything from drivers/block) but a USB blockdev and SD blockdev.
> 
> see the difference?

I assume I do, confirm above.

> the idea is that there would be no difference when working with
> SATA/PATA/SCSI (as the commands are almost the same currently), but
> working with USB drives and SD cards would be a little different (that is
> from their own separate commands, but not through the blockdev layer)

I see

> Pavel Herrmann

Best regards,
Marek Vasut