Re: [PATCH v2 6/8] drm/i915: Add function to output Aksv over GMBUS

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Dec 01, 2017 at 02:17:19PM -0500, Sean Paul wrote:
> On Fri, Dec 1, 2017 at 2:06 PM, Ville Syrjälä
> <ville.syrjala@linux.intel.com> wrote:
> > On Fri, Dec 01, 2017 at 12:20:28PM -0500, Sean Paul wrote:
> >> Once the Aksv is available in the PCH, we need to get it on the wire to
> >> the receiver via DDC. The hardware doesn't allow us to read the value
> >> directly, so we need to tell GMBUS to source the Aksv internally and
> >> send it to the right offset on the receiver.
> >>
> >> The way we do this is to initiate an indexed write where the index is
> >> the Aksv register offset. We write dummy values to GMBUS3 as if we were
> >> sending the key, and the hardware slips in the "real" values when it
> >> goes out.
> >>
> >> Changes in v2:
> >> - None
> >>
> >> Signed-off-by: Sean Paul <seanpaul@chromium.org>
> >> ---
> >>  drivers/gpu/drm/i915/i915_drv.h  |  1 +
> >>  drivers/gpu/drm/i915/i915_reg.h  |  1 +
> >>  drivers/gpu/drm/i915/intel_i2c.c | 54 ++++++++++++++++++++++++++++++++++------
> >>  3 files changed, 48 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> >> index 36bb4927484a..10f740c9e571 100644
> >> --- a/drivers/gpu/drm/i915/i915_drv.h
> >> +++ b/drivers/gpu/drm/i915/i915_drv.h
> >> @@ -4043,6 +4043,7 @@ extern int intel_setup_gmbus(struct drm_i915_private *dev_priv);
> >>  extern void intel_teardown_gmbus(struct drm_i915_private *dev_priv);
> >>  extern bool intel_gmbus_is_valid_pin(struct drm_i915_private *dev_priv,
> >>                                    unsigned int pin);
> >> +extern int intel_gmbus_output_aksv(struct i2c_adapter *adapter);
> >>
> >>  extern struct i2c_adapter *
> >>  intel_gmbus_get_adapter(struct drm_i915_private *dev_priv, unsigned int pin);
> >> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> >> index 6dca305ccbf7..8b71a20882ca 100644
> >> --- a/drivers/gpu/drm/i915/i915_reg.h
> >> +++ b/drivers/gpu/drm/i915/i915_reg.h
> >> @@ -3040,6 +3040,7 @@ enum i915_power_well_id {
> >>  # define GPIO_DATA_PULLUP_DISABLE    (1 << 13)
> >>
> >>  #define GMBUS0                       _MMIO(dev_priv->gpio_mmio_base + 0x5100) /* clock/port select */
> >> +#define   GMBUS_AKSV_SELECT  (1<<11)
> >>  #define   GMBUS_RATE_100KHZ  (0<<8)
> >>  #define   GMBUS_RATE_50KHZ   (1<<8)
> >>  #define   GMBUS_RATE_400KHZ  (2<<8) /* reserved on Pineview */
> >> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
> >> index eb5827110d8f..c01156bf0f27 100644
> >> --- a/drivers/gpu/drm/i915/intel_i2c.c
> >> +++ b/drivers/gpu/drm/i915/intel_i2c.c
> >> @@ -30,6 +30,7 @@
> >>  #include <linux/i2c-algo-bit.h>
> >>  #include <linux/export.h>
> >>  #include <drm/drmP.h>
> >> +#include <drm/drm_hdcp.h>
> >>  #include "intel_drv.h"
> >>  #include <drm/i915_drm.h>
> >>  #include "i915_drv.h"
> >> @@ -373,7 +374,8 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
> >>
> >>  static int
> >>  gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
> >> -                    unsigned short addr, u8 *buf, unsigned int len)
> >> +                    unsigned short addr, u8 *buf, unsigned int len,
> >> +                    u32 gmbus1_index)
> >>  {
> >>       unsigned int chunk_size = len;
> >>       u32 val, loop;
> >> @@ -386,7 +388,7 @@ gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
> >>
> >>       I915_WRITE_FW(GMBUS3, val);
> >>       I915_WRITE_FW(GMBUS1,
> >> -                   GMBUS_CYCLE_WAIT |
> >> +                   gmbus1_index | GMBUS_CYCLE_WAIT |
> >>                     (chunk_size << GMBUS_BYTE_COUNT_SHIFT) |
> >>                     (addr << GMBUS_SLAVE_ADDR_SHIFT) |
> >>                     GMBUS_SLAVE_WRITE | GMBUS_SW_RDY);
> >> @@ -409,7 +411,8 @@ gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
> >>  }
> >>
> >>  static int
> >> -gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
> >> +gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
> >> +              u32 gmbus1_index)
> >>  {
> >>       u8 *buf = msg->buf;
> >>       unsigned int tx_size = msg->len;
> >> @@ -419,7 +422,8 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
> >>       do {
> >>               len = min(tx_size, GMBUS_BYTE_COUNT_MAX);
> >>
> >> -             ret = gmbus_xfer_write_chunk(dev_priv, msg->addr, buf, len);
> >> +             ret = gmbus_xfer_write_chunk(dev_priv, msg->addr, buf, len,
> >> +                                          gmbus1_index);
> >>               if (ret)
> >>                       return ret;
> >>
> >> @@ -470,7 +474,8 @@ gmbus_xfer_index_read(struct drm_i915_private *dev_priv, struct i2c_msg *msgs)
> >>  }
> >>
> >>  static int
> >> -do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
> >> +do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num,
> >> +           u32 gmbus0_source, u32 gmbus1_index)
> >>  {
> >>       struct intel_gmbus *bus = container_of(adapter,
> >>                                              struct intel_gmbus,
> >> @@ -480,7 +485,7 @@ do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
> >>       int ret = 0;
> >>
> >>  retry:
> >> -     I915_WRITE_FW(GMBUS0, bus->reg0);
> >> +     I915_WRITE_FW(GMBUS0, gmbus0_source | bus->reg0);
> >>
> >>       for (; i < num; i += inc) {
> >>               inc = 1;
> >> @@ -490,7 +495,8 @@ do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
> >>               } else if (msgs[i].flags & I2C_M_RD) {
> >>                       ret = gmbus_xfer_read(dev_priv, &msgs[i], 0);
> >>               } else {
> >> -                     ret = gmbus_xfer_write(dev_priv, &msgs[i]);
> >> +                     ret = gmbus_xfer_write(dev_priv, &msgs[i],
> >> +                                            gmbus1_index);
> >>               }
> >>
> >>               if (!ret)
> >> @@ -598,7 +604,7 @@ gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
> >>               if (ret < 0)
> >>                       bus->force_bit &= ~GMBUS_FORCE_BIT_RETRY;
> >>       } else {
> >> -             ret = do_gmbus_xfer(adapter, msgs, num);
> >> +             ret = do_gmbus_xfer(adapter, msgs, num, 0, 0);
> >>               if (ret == -EAGAIN)
> >>                       bus->force_bit |= GMBUS_FORCE_BIT_RETRY;
> >>       }
> >> @@ -608,6 +614,38 @@ gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
> >>       return ret;
> >>  }
> >>
> >> +int intel_gmbus_output_aksv(struct i2c_adapter *adapter)
> >> +{
> >> +     struct intel_gmbus *bus = container_of(adapter, struct intel_gmbus,
> >> +                                            adapter);
> >> +     struct drm_i915_private *dev_priv = bus->dev_priv;
> >> +     int ret;
> >> +     u8 buf[DRM_HDCP_KSV_LEN] = { 0 };
> >> +     struct i2c_msg msg = {
> >> +             .addr = DRM_HDCP_DDC_ADDR,
> >> +             .flags = 0,
> >> +             .len = sizeof(buf),
> >> +             .buf = buf,
> >> +     };
> >> +
> >> +     intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);
> >> +     mutex_lock(&dev_priv->gmbus_mutex);
> >> +
> >> +     /*
> >> +      * In order to output Aksv to the receiver, use an indexed write to
> >> +      * pass the i2c command, and tell GMBUS to use the HW-provided value
> >> +      * instead of sourcing GMBUS3 for the data.
> >> +      */
> >> +     ret = do_gmbus_xfer(adapter, &msg, 1, GMBUS_AKSV_SELECT,
> >> +                         GMBUS_CYCLE_INDEX |
> >> +                         (DRM_HDCP_DDC_AKSV << GMBUS_SLAVE_INDEX_SHIFT));
> >
> > It might be nicer to just use two msgs here and modify
> > gmbus_xfer_index_read() to support indexed writes as well.
> 
> I think two msgs implies a STOP bit in between. At least, that's how I
> interpret "normal" writes.

There is never a step between two msgs AIUI, unless you specify
I2C_M_STOP. There might be a repeated start. If we want to be pedantic
about the repeated start we could use the I2C_M_NOSTART flag. Although
I don't think this stuff is really documented anywhere so I'm not sure
if I2C_M_NOSTART is really supposed to apply to two messages with the
same slave address and same direction, or if it's just meant to
suppress the repeated start when changing the direction of the bus
(which gmbus can't do, and we actually fail to check for that).

I suppose i2c-algo-bit is the defacto standard here. And that one
seems to do the repeated start whenever I2C_M_NOSTART is not specified.
Would be actually nice to know what gmbus does when you just do two
back to back non-indexed writes to the same slave address. If it
doesn't do a repeated start in between, then I guess we're also
violating I2C_M_NOSTART currently.

> 
> > Would avoid having to pass in the GMBUS1 value all the way.
> 
> We could infer an indexed write if num_msgs == 1 && flags == 0 && len
> > 1. However that would require us to assume that all single msg
> writes have a command byte at the beginning of the transaction, which
> might not be true for all i2c slaves.
> 
> Sean
> 
> 
> >
> > Not sure what to do with GMBUS_AKSV_SELECT. I guess either pass
> > it in explicitly like you're doing here, or maybe add a small
> > helper ala gmbus_is_index_read() so that do_gmbus_xfer() could
> > sniff out which source we should use based on the passed in msgs?
> >
> >> +
> >> +     mutex_unlock(&dev_priv->gmbus_mutex);
> >> +     intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS);
> >> +
> >> +     return ret;
> >> +}
> >> +
> >>  static u32 gmbus_func(struct i2c_adapter *adapter)
> >>  {
> >>       return i2c_bit_algo.functionality(adapter) &
> >> --
> >> 2.15.0.531.g2ccb3012c9-goog
> >>
> >> _______________________________________________
> >> dri-devel mailing list
> >> dri-devel@lists.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >
> > --
> > Ville Syrjälä
> > Intel OTC

-- 
Ville Syrjälä
Intel OTC