From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marek Vasut <marex@denx.de>
Date: Fri, 21 Sep 2012 17:34:27 +0200
Subject: [U-Boot] [PATCH 01/11] DM: add block device core
In-Reply-To: <56183164.uZ3HcVocPu@bloomfield>
References: <1348169867-2917-1-git-send-email-morpheus.ibis@gmail.com>
	<201209211553.26375.marex@denx.de> <56183164.uZ3HcVocPu@bloomfield>
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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?

> > > 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?

> > > - 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.

> 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