[Bug 14310] [bisected] 2.6.31 regression sis5513 PIO Mode 0 hang

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http://bugzilla.kernel.org/show_bug.cgi?id=14310





--- Comment #8 from David S. Miller <davem@davemloft.net>  2009-11-06 12:51:46 ---
From: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Date: Thu, 5 Nov 2009 16:54:27 +0100

> The problem is that the change in the debug patch affects all host drivers
> and at this moment is not safe enough neither for -stable nor for -rc.
> 
> Somebody needs to go and review all host drivers and their usage of ->media
> field for tuning logic present in ->set_pio_mode implementations first.

The drivers which do this are:

drivers/ide/alim15x3.c
drivers/ide/it8172.c
drivers/ide/it8213.c
drivers/ide/pdc202xx_old.c
drivers/ide/piix.c
drivers/ide/qd65xx.c
drivers/ide/sis5513.c
drivers/ide/slc90e66.c

While the majority of them seem to use it to decide whether to enable
prefetching or not, alim15x3.c uses the ->media value to decide
whether to turn on the ATA or the ATAPI FIFO.

I don't think it's safe to call ->set_pio_mode() until we actually
know the media type.

I suppose we could guard the prefetch/FIFO changes in these drivers
with a test like:

    if (!(hwif->port_flags & IDE_PFLAG_PROBING))

or something like that.

But in this stage of the game, it's just too risky and reverting
the early PIO0 commit is the best way to go.

I'll do that now.

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