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Re: [Qemu-devel] [RFC 0/7] Convert SD card model to AIO

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [RFC 0/7] Convert SD card model to AIO
Date: Mon, 13 May 2013 14:13:54 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

On Fri, May 10, 2013 at 08:10:18PM +0400, Igor Mitsyanko wrote:
> This is an initial attempt to change our SD card model to use asynchronious
> input/output API instead of synchronious one. This will require converting of
> every user also. Right now I've converted only PL181 model, and I'll wait
> for some feedback on taken approach before I'll continue with other users.
> New async SD interface is built on two callbacks:
> 1 Callback which models arrival of start bit on DAT line from card (start bit)
> 2 Callback modeling deasserting of DAT0 line by card when it has finished
> programming data (data busy end)
> This is based on SD card specification.
> Start bit is issued for every new block of data coming from card.
> DAT0 line is kept low by card to signal busy state, while data block is being
> programmed by card and it can't receive new data.
> Furthermore, I decided to drop data buffering on SD controller side. We 
> already
> have two buffers in SD card model, no need to have another one in controller 
> model.
> We can avoid intermediate copying from card's buffer to controller's buffer, 
> and
> read/write directly from card.
> Tested by running this Fedora image 
> https://fedoraproject.org/wiki/Architectures/ARM/F18/Versatile_Express
> on versatile board.
> Igor Mitsyanko (7):
>   sd.c: introduce AIO related members in SD state
>   sd.c: introduce variable for trekking valid data
>   sd.c: introduce "start bit" and "busy deasserted" callbacks
>   sd.c: use callbacks as a flag to use async IO
>   sd.c: introduce async read operation
>   sd.c: introduce async write interface
>   pl181.c: convert to async IO SD card interface
>  hw/sd/omap_mmc.c    |   6 +-
>  hw/sd/pl181.c       | 302 
> +++++++++++++++++++++++++++++++++-------------------
>  hw/sd/pxa2xx_mmci.c |   2 +-
>  hw/sd/sd.c          | 272 ++++++++++++++++++++++++++++++++++++++++++----
>  hw/sd/sdhci.c       |   4 +-
>  include/hw/sd.h     |   3 +-
>  6 files changed, 449 insertions(+), 140 deletions(-)

Thanks for doing this!  It makes me happy when we replace synchronous
block layer callers with asynchronous ones.

I didn't review each line but overall it seems like the right direction.


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