[Intel-gfx] [RFC 1/2] drm/i915/gmbus: Increase the Bytes per Rd/Wr Op

[Jani Nikula]

On Thu, 12 Apr 2018, Ramalingam C <ramalingam.c at intel.com> wrote:
> From BXT onwards Bspec says HW supports Max Bytes per single RD/WR op is
> 511Bytes instead of previous 256Bytes used in SW.

"BXT onwards" and "SKL onwards" are always slightly confusing, because
it's not always clear if one includes the other. Since the code is
written gen 9+, perhaps use that here and in the macro definition too?

>
> This change allows the max bytes per op upto 511Bytes from BXT onwards.
>
> Cc: Jani Nikula <jani.nikula at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Ramalingam C <ramalingam.c at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reg.h  |  1 +
>  drivers/gpu/drm/i915/intel_i2c.c | 10 ++++++++--
>  2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 475cac07d3e6..4f583da0cee9 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -3013,6 +3013,7 @@ enum i915_power_well_id {
>  #define   GMBUS_CYCLE_STOP	(4<<25)
>  #define   GMBUS_BYTE_COUNT_SHIFT 16
>  #define   GMBUS_BYTE_COUNT_MAX   256U
> +#define   BXT_GMBUS_BYTE_COUNT_MAX 511U
>  #define   GMBUS_SLAVE_INDEX_SHIFT 8
>  #define   GMBUS_SLAVE_ADDR_SHIFT 1
>  #define   GMBUS_SLAVE_READ	(1<<0)
> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
> index e6875509bcd9..7e92c7934657 100644
> --- a/drivers/gpu/drm/i915/intel_i2c.c
> +++ b/drivers/gpu/drm/i915/intel_i2c.c
> @@ -400,7 +400,10 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
>  	int ret;
>  
>  	do {
> -		len = min(rx_size, GMBUS_BYTE_COUNT_MAX);
> +		if (INTEL_GEN(dev_priv) >= 9)
> +			len = min(rx_size, BXT_GMBUS_BYTE_COUNT_MAX);
> +		else
> +			len = min(rx_size, GMBUS_BYTE_COUNT_MAX);
>  
>  		ret = gmbus_xfer_read_chunk(dev_priv, msg->addr,
>  					    buf, len, gmbus1_index);
> @@ -462,7 +465,10 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
>  	int ret;
>  
>  	do {
> -		len = min(tx_size, GMBUS_BYTE_COUNT_MAX);
> +		if (INTEL_GEN(dev_priv) >= 9)
> +			len = min(tx_size, BXT_GMBUS_BYTE_COUNT_MAX);
> +		else
> +			len = min(tx_size, GMBUS_BYTE_COUNT_MAX);
>  
>  		ret = gmbus_xfer_write_chunk(dev_priv, msg->addr, buf, len,
>  					     gmbus1_index);

-- 
Jani Nikula, Intel Open Source Technology Center