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viafb: don't touch clock state on OLPC XO-1.5

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As detailed in the thread titled "viafb PLL/clock tweaking causes XO-1.5
instability," enabling or disabling the IGA1/IGA2 clocks causes occasional
stability problems during suspend/resume cycles on this platform.

This is rather odd, as the documentation suggests that clocks have two
states (on/off) and the default (stable) configuration is configured to
enable the clock only when it is needed. However, explicitly enabling *or*
disabling the clock triggers this system instability, suggesting that there
is a 3rd state at play here.

Leaving the clock enable/disable registers alone solves this problem.
This fixes spurious reboots during suspend/resume behaviour introduced by
commit b692a63a.

Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: stable@vger.kernel.org
This commit is contained in:
Daniel Drake 2012-09-04 11:45:32 -04:00 committed by Florian Tobias Schandinat
parent e75478bbd7
commit 012a121184
1 changed files with 19 additions and 0 deletions
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19
drivers/video/via/via_clock.c
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@ -25,6 +25,7 @@
#include <linux/kernel.h>
#include <linux/via-core.h>
#include <asm/olpc.h>
#include "via_clock.h"
#include "global.h"
#include "debug.h"
@ -289,6 +290,10 @@ static void dummy_set_pll(struct via_pll_config config)
printk(KERN_INFO "Using undocumented set PLL.\n%s", via_slap);
}
static void noop_set_clock_state(u8 state)
{
}
void via_clock_init(struct via_clock *clock, int gfx_chip)
{
switch (gfx_chip) {
@ -346,4 +351,18 @@ void via_clock_init(struct via_clock *clock, int gfx_chip)
break;
}
if (machine_is_olpc()) {
/* The OLPC XO-1.5 cannot suspend/resume reliably if the
* IGA1/IGA2 clocks are set as on or off (memory rot
* occasionally happens during suspend under such
* configurations).
*
* The only known stable scenario is to leave this bits as-is,
* which in their default states are documented to enable the
* clock only when it is needed.
*/
clock->set_primary_clock_state = noop_set_clock_state;
clock->set_secondary_clock_state = noop_set_clock_state;
}
}