Re: [PATCH 2/2] drm/i915: abstract i2c bit banging fallback in gmbus xfer

Ville Syrjälä
2015-12-01T14:57:24Z

On Tue, Dec 01, 2015 at 04:29:26PM +0200, Jani Nikula wrote:
> Choose between i2c bit banging and gmbus in a new higher level function,
> and let the i2c core retry the first time we fall back to bit banging.
>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
> drivers/gpu/drm/i915/intel_i2c.c | 39 +++++++++++++++++++++++++--------------
> 1 file changed, 25 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
> index ccb522c176bd..e26e22a72e3b 100644
> --- a/drivers/gpu/drm/i915/intel_i2c.c
> +++ b/drivers/gpu/drm/i915/intel_i2c.c
> @@ -472,9 +472,7 @@ gmbus_xfer_index_read(struct drm_i915_private *dev_priv, struct i2c_msg *msgs)
> }
>
> static int
> -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)
> {
> struct intel_gmbus *bus = container_of(adapter,
> struct intel_gmbus,
> @@ -483,14 +481,6 @@ gmbus_xfer(struct i2c_adapter *adapter,
> int i = 0, inc, try = 0;
> int ret = 0;
>
> - intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);
> - mutex_lock(&dev_priv->gmbus_mutex);
> -
> - if (bus->force_bit) {
> - ret = i2c_bit_algo.master_xfer(adapter, msgs, num);
> - goto out;
> - }
> -
> retry:
> I915_WRITE(GMBUS0, bus->reg0);
>
> @@ -585,13 +575,34 @@ timeout:
> bus->adapter.name, bus->reg0 & 0xff);
> I915_WRITE(GMBUS0, 0);
>
> - /* Hardware may not support GMBUS over these pins? Try GPIO bitbanging instead. */
> + /*
> + * Hardware may not support GMBUS over these pins? Try GPIO bitbanging
> + * instead. Use EAGAIN to have i2c core retry.
> + */
> bus->force_bit = 1;
> - ret = i2c_bit_algo.master_xfer(adapter, msgs, num);
> + ret = -EAGAIN;

This does mean we're left to the mercy of the timeout handling in the
i2c core. That is if our gmbus attempt takes too long, we may never
get a chance to retry with bit banging. Not sure if that's a real
concern or not.

Otherwise lgtm.

>
> out:
> - mutex_unlock(&dev_priv->gmbus_mutex);
> + return ret;
> +}
> +
> +static int
> +gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
> +{
> + struct intel_gmbus *bus = container_of(adapter, struct intel_gmbus,
> + adapter);
> + struct drm_i915_private *dev_priv = bus->dev_priv;
> + int ret;
> +
> + intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);
> + mutex_lock(&dev_priv->gmbus_mutex);
> +
> + if (bus->force_bit)
> + ret = i2c_bit_algo.master_xfer(adapter, msgs, num);
> + else
> + ret = do_gmbus_xfer(adapter, msgs, num);
>
> + mutex_unlock(&dev_priv->gmbus_mutex);
> intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS);
>
> return ret;
> --
> 2.1.4
>
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--
Ville Syrjälä
Intel OTC