Date: Thu, 22 Jan 2009 09:05:40 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: mav@FreeBSD.org Cc: freebsd-arm@FreeBSD.org, ticso@cicely.de Subject: Re: Mount root from SD card? Message-ID: <20090122.090540.-839781195.imp@bsdimp.com> In-Reply-To: <49787314.3070004@FreeBSD.org> References: <20090121.122842.-1582190967.imp@bsdimp.com> <20090122105650.GB50103@cicely7.cicely.de> <49787314.3070004@FreeBSD.org>
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In message: <49787314.3070004@FreeBSD.org>
Alexander Motin <mav@freebsd.org> writes:
: Bernd Walter wrote:
: > On Wed, Jan 21, 2009 at 12:28:42PM -0700, M. Warner Losh wrote:
: >> In message: <49776734.8030805@FreeBSD.org>
: >> Alexander Motin <mav@FreeBSD.org> writes:
: >> :
: >> : This part looks quire strange for plain FIFO explanation. Several
: >> : consequential commands give different results:
: >> :
: >> : CMD: 37 ARG 10000 len 0
: >> : RES: 0
: >> : CMD: d ARG 0 len 64
: >> :
: >> : ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 28
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...
: >> : RES: 2
: >> : CMD: 37 ARG 10000 len 0
: >> : RES: 0
: >> : CMD: d ARG 0 len 64
: >> :
: >> : ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00
: >> : 00 00 00 28 00 00 00 00 00 00 00 00 00 00 00 00
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...
: >> : RES: 2
: >> : CMD: 37 ARG 10000 len 0
: >> : RES: 0
: >> : CMD: d ARG 0 len 64
: >> :
: >> : ff ff ff ff 00 00 00 00 00 00 00 28 00 00 00 00
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...
: >> : RES: 2
: >> : CMD: 37 ARG 10000 len 0
: >> : RES: 0
: >> : CMD: d ARG 0 len 64
: >> :
: >> : ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 28
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
: >> : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...
: >> : RES: 2
: >> :
: >> : While working on sdhci driver for on ENE chip I have found that for
: >> : short transfers (less then 1K) DMA engine returns set of zeroes instead
: >> : of data. I haven't found better solution and just handling short
: >> : transfers by PIO. Same problem exists for PIO also, but there it was
: >> : masked by adding short delay before reading from port.
: >>
: >> I'll have to take a look at the code in more detail to make sure that
: >> we're doing the right thing. I noticed all the ff's, but didn't
: >> notice until now what they were shifted the same way that the data
: >> blocks were later. In this case, you'll see there's three of them.
: >>
: >> I believe that this is the first use of a CMD that generates data that
: >> isn't a full block of data...
: >
: > Havn't read everything, so maybe I writing nonsense in respect to
: > this problem.
: > The multiblock read trouble is a problem in the MMC design.
: > The first read always works fine, but you need to stop the transfer
: > and an exact time, otherwise it starts reading the next block.
: > The first bytes of the next block then stucks in the DMA fifo and
: > the next read then starts with the stuck uint32.
: > If you see broken reads like this then I would assume the previous
: > command was problematic.
: > The official workaround to get multiblock reading is to reset the MMC
: > and clean the fifo after each multiblock command, but I would assume
: > it is enough to just read the data register a few time before setting
: > up the DMA for the new request.
:
: Haven't look deep at that arm controller operation, but standard SD host
: has special counter register which terminates DMA transfer after
: specified amount of blocks. sdhci driver even uses it's Auth-CMD12
: feature, where controller even sends STOP command to the card by itself.
The standard host adapter spec has this. The Atmel part doesn't.
Warner
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