linux-kernel - Re: [PATCH v4 6/9] drm/i915: Make use of indexed write GMBUS feature

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Message-ID: <20171207084737.irp5cqw4jeh2sms5@phenom.ffwll.local>
Date:   Thu, 7 Dec 2017 09:47:37 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Sean Paul <seanpaul@...omium.org>
Cc:     dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, daniel.vetter@...el.com,
        seanpaul@...gle.com, ramalingam.c@...el.com,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH v4 6/9] drm/i915: Make use of indexed write GMBUS feature

On Wed, Dec 06, 2017 at 07:00:09PM -0500, Sean Paul wrote:
> This patch enables the indexed write feature of the GMBUS to concatenate
> 2 consecutive messages into one. The criteria for an indexed write is
> that both messages are writes, the first is length == 1, and the second
> is length > 0. The first message is sent out by the GMBUS as the slave
> command, and the second one is sent via the GMBUS FIFO as usual.
> 
> Changes in v3:
> - Added to series
> Changes in v4:
> - Combine indexed reads and writes (Ville)
> 
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> Suggested-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> Signed-off-by: Sean Paul <seanpaul@...omium.org>

Even prettier!

Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>

> ---
>  drivers/gpu/drm/i915/intel_i2c.c | 34 ++++++++++++++++++++--------------
>  1 file changed, 20 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
> index 49fdf09f9919..d78ce758fbfa 100644
> --- a/drivers/gpu/drm/i915/intel_i2c.c
> +++ b/drivers/gpu/drm/i915/intel_i2c.c
> @@ -373,7 +373,8 @@ 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 +387,7 @@ 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 +410,8 @@ 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 +421,8 @@ 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;
>  
> @@ -431,21 +434,21 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
>  }
>  
>  /*
> - * The gmbus controller can combine a 1 or 2 byte write with a read that
> - * immediately follows it by using an "INDEX" cycle.
> + * The gmbus controller can combine a 1 or 2 byte write with another read/write
> + * that immediately follows it by using an "INDEX" cycle.
>   */
>  static bool
> -gmbus_is_index_read(struct i2c_msg *msgs, int i, int num)
> +gmbus_is_index_xfer(struct i2c_msg *msgs, int i, int num)
>  {
>  	return (i + 1 < num &&
>  		msgs[i].addr == msgs[i + 1].addr &&
>  		!(msgs[i].flags & I2C_M_RD) &&
>  		(msgs[i].len == 1 || msgs[i].len == 2) &&
> -		(msgs[i + 1].flags & I2C_M_RD));
> +		msgs[i + 1].len > 0);
>  }
>  
>  static int
> -gmbus_xfer_index_read(struct drm_i915_private *dev_priv, struct i2c_msg *msgs)
> +gmbus_index_xfer(struct drm_i915_private *dev_priv, struct i2c_msg *msgs)
>  {
>  	u32 gmbus1_index = 0;
>  	u32 gmbus5 = 0;
> @@ -462,7 +465,10 @@ gmbus_xfer_index_read(struct drm_i915_private *dev_priv, struct i2c_msg *msgs)
>  	if (gmbus5)
>  		I915_WRITE_FW(GMBUS5, gmbus5);
>  
> -	ret = gmbus_xfer_read(dev_priv, &msgs[1], gmbus1_index);
> +	if (msgs[1].flags & I2C_M_RD)
> +		ret = gmbus_xfer_read(dev_priv, &msgs[1], gmbus1_index);
> +	else
> +		ret = gmbus_xfer_write(dev_priv, &msgs[1], gmbus1_index);
>  
>  	/* Clear GMBUS5 after each index transfer */
>  	if (gmbus5)
> @@ -486,13 +492,13 @@ do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
>  
>  	for (; i < num; i += inc) {
>  		inc = 1;
> -		if (gmbus_is_index_read(msgs, i, num)) {
> -			ret = gmbus_xfer_index_read(dev_priv, &msgs[i]);
> -			inc = 2; /* an index read is two msgs */
> +		if (gmbus_is_index_xfer(msgs, i, num)) {
> +			ret = gmbus_index_xfer(dev_priv, &msgs[i]);
> +			inc = 2; /* an index transmission is two msgs */
>  		} 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], 0);
>  		}
>  
>  		if (!ret)
> -- 
> 2.15.1.424.g9478a66081-goog
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch