Re: [PATCH 2.6.30] iwl3945: fix rfkill switch

[reinette chatre <reinette.chatre@intel.com>]

Hi Stanislaw,

On Thu, 2009-08-06 at 00:19 -0700, Stanislaw Gruszka wrote:
> On Wed, Aug 05, 2009 at 03:51:49PM -0700, reinette chatre wrote:
> > On Tue, 2009-08-04 at 05:35 -0700, Stanislaw Gruszka wrote:
> > > Due to rfkill and iwlwifi mishmash of SW / HW killswitch representation,
> > > we have race conditions which make unable turn wifi radio on, after enable
> > > and disable again killswitch. I can observe this problem on my laptop
> > > with iwl3945 device.
> > > 
> > > In rfkill core HW switch and SW switch are separate 'states'. Device can
> > > be only in one of 3 states: RFKILL_STATE_SOFT_BLOCKED, RFKILL_STATE_UNBLOCKED,
> > > RFKILL_STATE_HARD_BLOCKED. Whereas in iwlwifi driver we have separate bits
> > > STATUS_RF_KILL_HW and STATUS_RF_KILL_SW for HW and SW switches - radio can be
> > > turned on, only if both bits are cleared.
> > > 
> > > In this particular race conditions, radio can not be turned on if in driver
> > > STATUS_RF_KILL_SW bit is set, and rfkill core is in state
> > > RFKILL_STATE_HARD_BLOCKED, because rfkill core is unable to call
> > > rfkill->toggle_radio(). This situation can be entered in case:
> > > 
> > 
> > I am trying to understand this race condition ...
> > 
> > > - killswitch is turned on
> > > - rfkill core 'see' button change first and move to RFKILL_STATE_SOFT_BLOCKED
> > >   also call ->toggle_radio() and STATE_RF_KILL_SW in driver is set
> > > - iwl3945 get info about button from hardware to set STATUS_RF_KILL_HW bit and
> > >   force rfkill to move to RFKILL_STATE_HARD_BLOCKED
> > 
> > ok - so at this point we have rfkill == RFKILL_STATE_HARD_BLOCKED, and
> > driver == STATE_RF_KILL_SW | STATE_RF_KILL_HW
> > 
> > > - killsiwtch is turend off
> 
> Here rfkill core routines are called. Rfkill wants to clear STATUS_RF_KILL_SW
> but it can not as state is RFKILL_STATE_HARD_BLOCKED.
> 
> > > - driver clear STATUS_RF_KILL_HW
> > 
> > at this point the driver should clear STATE_RF_KILL_HW and then call
> > iwl_rfkill_set_hw_state(). From what I can tell, in
> > iwl_rfkill_set_hw_state() the test for iwl_is_rfkill_sw() will cause the
> > driver to call rfkill_force_state for RFKILL_STATE_SOFT_BLOCKED
> > 
> > So, from what I understand after the above the status will be
> > 
> > rfkill == RFKILL_STATE_SOFT_BLOCKED, and driver == STATE_RF_KILL_SW 
> 
> Thats right. But rfkill core no longer wants to manipulate state via
> ->toggle_radio() and radio stays disabled.
>  
> > > - rfkill core is unable to clear STATUS_RF_KILL_SW in driver
> > 
> > I do not understand why this is a problem here. Could you please
> > highlight what I am missing?
> 
> In my description I miss the most important part, sorry. Race is when the
> switches are performed in that order:
> 
> Radio enabled 
> - rfkill SW on
> - driver HW on
> Radio disabled - ok
> - rfkill SW off <- problem not clearing STATUS_RF_KILL_SW
> - driver HW off
> Radio disabled - wrong 
> 
> Everything is fine when actions are in that order:
> 
> Radio enabled
> - rfkill SW on
> - driver HW on
> Radio disabled - ok 
> - driver HW off
> - rfkill SW off
> Radio enabled - ok 


Thanks for the explanation.

> 
> > > 
> > > Additionally call to rfkill_epo() when STATUS_RF_KILL_HW in driver is set
> > > cause move to the same situation.
> > > 
> > > In 2.6.31 this problem is fixed due to _total_ rewrite of rfkill subsystem.
> > > This is a quite small fix for 2.6.30.x in iwl3945 driver. We disable
> > > STATUS_RF_KILL_SW bit regardless of HW bit state. Also report to rfkill
> > > subsystem SW switch bit before HW switch bit to move rfkill subsystem
> > > to SOFT_BLOCK rather than HARD_BLOCK.
> > > 
> > > Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
> > > ---
> > > I'm not sure if this is good candidate for stable as this is not backport
> > > of upstream commit. Also I did not test this patch with other iwlwifi devices,
> > > only with iwl3945.
> > > 
> > >  drivers/net/wireless/iwlwifi/iwl-rfkill.c |   24 ++++++++++++++----------
> > >  1 files changed, 14 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/drivers/net/wireless/iwlwifi/iwl-rfkill.c b/drivers/net/wireless/iwlwifi/iwl-rfkill.c
> > > index 2ad9faf..d6b6098 100644
> > > --- a/drivers/net/wireless/iwlwifi/iwl-rfkill.c
> > > +++ b/drivers/net/wireless/iwlwifi/iwl-rfkill.c
> > > @@ -54,21 +54,28 @@ static int iwl_rfkill_soft_rf_kill(void *data, enum rfkill_state state)
> > >  	case RFKILL_STATE_UNBLOCKED:
> > >  		if (iwl_is_rfkill_hw(priv)) {
> > >  			err = -EBUSY;
> > > -			goto out_unlock;
> > > +			/* pass error to rfkill core to make it state HARD
> > > +			 * BLOCKED and disable software kill switch */
> > >  		}
> > >  		iwl_radio_kill_sw_enable_radio(priv);
> > >  		break;
> > >  	case RFKILL_STATE_SOFT_BLOCKED:
> > >  		iwl_radio_kill_sw_disable_radio(priv);
> > > +		/* rfkill->mutex lock is taken */
> > > +		if (priv->rfkill->state == RFKILL_STATE_HARD_BLOCKED) {
> > > +			/* force rfkill core state to be SOFT BLOCKED,
> > > +			 * otherwise core will be unable to disable software
> > > +			 * kill switch */
> > > +			priv->rfkill->state = RFKILL_STATE_SOFT_BLOCKED;
> > > +		}
> > 
> > I understand that you are directly changing the rfkill internals because
> > the mutex is taken ... but this really does not seem right to directly
> > modify the rfkill state in this way.
> 
> Agree this is dirty hack, but I did not find a better way. Eventually,
> if we add call to rfkill_uevent(), this would behave the same
> as rfkill_force_state() .

Sorry, but I really do not understand why this code is needed. From what
you say rfkill can be in one of three states: RFKILL_STATE_UNBLOCKED,
RFKILL_STATE_SOFT_BLOCKED, or RFKILL_STATE_HARD_BLOCKED. From what I
understand the above code is called when there is an rfkill state change
and the new state is provided. So, only _one_ of the three states will
be provided as parameter. This state is then tested - so in the case
that you modified here the state has already been tested to be
RFKILL_STATE_SOFT_BLOCKED. How is it thus possible that it can be
RFKILL_STATE_HARD_BLOCKED also?

Reinette