Re: [PATCH v2] drm/i915: BXT DDI PHY sequence BUN

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 31 Mar 2016, Imre Deak <imre.deak@intel.com> wrote:
> On to, 2016-03-31 at 19:47 +0300, Kannan, Vandana wrote:
>> > -----Original Message-----
>> > From: Deak, Imre
>> > Sent: Thursday, March 31, 2016 9:45 AM
>> > To: Kannan, Vandana <vandana.kannan@intel.com>; intel-
>> > gfx@lists.freedesktop.org
>> > Cc: Nikula, Jani <jani.nikula@intel.com>
>> > Subject: Re: [PATCH v2] drm/i915: BXT DDI PHY sequence BUN
>> > 
>> > On to, 2016-03-31 at 22:40 +0530, Vandana Kannan wrote:
>> > > According to the BSpec update, bit 7 of PORT_CL1CM_DW0 register
>> > needs
>> > > to be checked to ensure that the register is in accessible state.
>> > > Also, based on a BSpec update, changing the timeout value to check
>> > > iphypwrgood, from 10ms to wait for up to 100us.
>> > > 
>> > > v2: use wait_for_us instead of the atomic call.
>> > > 
>> > > Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
>> > > Reported-by: Philippe Lecluse <Philippe.Lecluse@intel.com>
>> > > Cc: Deak, Imre <imre.deak@intel.com>
>> > > Cc: Nikula, Jani <jani.nikula@intel.com>
>> > > ---
>> > >  drivers/gpu/drm/i915/i915_reg.h  |  1 +
>> > >  drivers/gpu/drm/i915/intel_ddi.c | 15 +++++++++++++--
>> > >  2 files changed, 14 insertions(+), 2 deletions(-)
>> > > 
>> > > diff --git a/drivers/gpu/drm/i915/i915_reg.h
>> > > b/drivers/gpu/drm/i915/i915_reg.h index 7dfc400..9a02bfc 100644
>> > > --- a/drivers/gpu/drm/i915/i915_reg.h
>> > > +++ b/drivers/gpu/drm/i915/i915_reg.h
>> > > @@ -1318,6 +1318,7 @@ enum skl_disp_power_wells {
>> > >  #define _PORT_CL1CM_DW0_A		0x162000
>> > >  #define _PORT_CL1CM_DW0_BC		0x6C000
>> > >  #define   PHY_POWER_GOOD		(1 << 16)
>> > > +#define   PHY_RESERVED			(1 << 7)
>> > >  #define BXT_PORT_CL1CM_DW0(phy)		_BXT_PHY((phy),
>> > _PORT_CL1CM_DW0_BC, \
>> > >  							_PORT_CL1CM_DW0_A)
>> > > 
>> > > diff --git a/drivers/gpu/drm/i915/intel_ddi.c
>> > > b/drivers/gpu/drm/i915/intel_ddi.c
>> > > index 62de9f4..05a5b3a 100644
>> > > --- a/drivers/gpu/drm/i915/intel_ddi.c
>> > > +++ b/drivers/gpu/drm/i915/intel_ddi.c
>> > > @@ -2669,9 +2669,20 @@ static void broxton_phy_init(struct
>> > drm_i915_private *dev_priv,
>> > >  	val |= GT_DISPLAY_POWER_ON(phy);
>> > >  	I915_WRITE(BXT_P_CR_GT_DISP_PWRON, val);
>> > > 
>> > > -	/* Considering 10ms timeout until BSpec is updated */
>> > > -	if (wait_for(I915_READ(BXT_PORT_CL1CM_DW0(phy)) &
>> > PHY_POWER_GOOD, 10))
>> > > +	/*
>> > > +	 * The PHY registers start out inaccessible and respond to reads
>> > with
>> > > +	 * all 1s.  Eventually they become accessible as they power up, then
>> > > +	 * the reserved bit will give the default 0.  Poll on the reserved bit
>> > > +	 * becoming 0 to find when the PHY is accessible.
>> > > +	 * HW team confirmed that the time to reach phypowergood status
>> > is
>> > > +	 * anywhere between 50 us and 100us.
>> > > +	 */
>> > > +	if (wait_for_us(((!(I915_READ(BXT_PORT_CL1CM_DW0(phy)) &
>> > > +				PHY_RESERVED)) &&
>> > > +				((I915_READ(BXT_PORT_CL1CM_DW0(phy)) &
>> > > +				  PHY_POWER_GOOD) ==
>> > PHY_POWER_GOOD)), 100)) {
>> > >  		DRM_ERROR("timeout during PHY%d power on\n", phy);
>> > 
>> > Thanks. This is still missing Jani's comment, that is reading out the register
>> > only once and applying a mask before comparing against
>> > PHY_POWER_GOOD.
>> > 
>> > --Imre
>> > 
>> [Vandana] 
>> Oh! Thought he said its fine on an updated mail.
>
> Hm, if you check below,
>
>> 
>> "
>> > > +	if (wait_for_atomic_us(((!(I915_READ(BXT_PORT_CL1CM_DW0(phy)) &
>> > > +				PHY_RESERVED)) &&
>> > > +				((I915_READ(BXT_PORT_CL1CM_DW0(phy)) &
>> > > +				  PHY_POWER_GOOD) == PHY_POWER_GOOD)), 100)) {
>> > 
>> > Is there any reason why you'd need to do the read twice? Why not just 
>> > write it as:
>> > 

This is the condition I meant:

>> > (I915_READ(BXT_PORT_CL1CM_DW0(phy)) & (PHY_RESERVED | PHY_POWER_GOOD)) 
>> > == PHY_POWER_GOOD
>> 
>> AFAICT this should be fine.
>
> This just means what I also asked. I'd prefer this, since reading out the
> register twice is redundant and makes the reader wonder why it was needed
> in the first place.

Exactly, so I wrote the condition as I would write it, and meant *it*
should be fine, i.e. with just one read of BXT_PORT_CL1CM_DW0.

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Technology Center
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