Re: [PATCH 3.12 071/142] drm/i915: cope with large i2c transfers

[Luis Henriques <luis.henriques@canonical.com>]

On Mon, May 18, 2015 at 02:00:04PM +0300, Jani Nikula wrote:
> On Mon, 18 May 2015, Jani Nikula <jani.nikula@intel.com> wrote:
> > On Mon, 18 May 2015, Luis Henriques <luis.henriques@canonical.com> wrote:
> >> On Sat, May 16, 2015 at 09:37:11AM +0200, Jiri Slaby wrote:
> >>> From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> >>> 
> >>> 3.12-stable review patch.  If anyone has any objections, please let me know.
> >>> 
> >>
> >> Ben Hutchings (on CC) just asked about this patch being included on
> >> the 3.16 kernel [1].  Is this patch really useful for kernels < 3.17?
> >> Should it be reverted from all the other stable kernels (3.10, 3.14
> >> and 3.16), or do you think it's harmless?
> >
> > The bug fixed by Dmitry's patch has been there since the introduction of
> > the gmbus code in v2.6.37 by
> >
> > commit f899fc64cda8569d0529452aafc0da31c042df2e
> > Author: Chris Wilson <chris@chris-wilson.co.uk>
> > Date:   Tue Jul 20 15:44:45 2010 -0700
> >
> >     drm/i915: use GMBUS to manage i2c links
> >
> > It's just that nobody noticed before
> >
> > commit 9d8dc3e529a19e427fd379118acd132520935c5d
> > Author: Nick Dyer <nick.dyer@itdev.co.uk>
> > Date:   Wed Jul 23 12:49:04 2014 -0700
> >
> >     Input: atmel_mxt_ts - implement T44 message handling
> 
> So to be clear, I think the fix is worth backporting anywhere you can
> easily backport. I did not check, but I think it may be possible to
> trigger this from userspace with the i2c interface.
> 
> 

Great, so it's definitely worth keeping it in all these stable trees.
Thanks a lot for the clarification, Jani.

Cheers,
--
Luís

> >
> >
> > BR,
> > Jani.
> >
> >
> >>
> >> [1] http://thread.gmane.org/gmane.linux.kernel.stable/136673
> >>
> >> Cheers,
> >> --
> >> Luís
> >>
> >>> ===============
> >>> 
> >>> commit 9535c4757b881e06fae72a857485ad57c422b8d2 upstream.
> >>> 
> >>> The hardware, according to the specs, is limited to 256 byte transfers,
> >>> and current driver has no protections in case users attempt to do larger
> >>> transfers. The code will just stomp over status register and mayhem
> >>> ensues.
> >>> 
> >>> Let's split larger transfers into digestable chunks. Doing this allows
> >>> Atmel MXT driver on Pixel 1 function properly (it hasn't since commit
> >>> 9d8dc3e529a19e427fd379118acd132520935c5d "Input: atmel_mxt_ts -
> >>> implement T44 message handling" which tries to consume multiple
> >>> touchscreen/touchpad reports in a single transaction).
> >>> 
> >>> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> >>> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> >>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> >>> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> >>> ---
> >>>  drivers/gpu/drm/i915/i915_reg.h  |  1 +
> >>>  drivers/gpu/drm/i915/intel_i2c.c | 66 ++++++++++++++++++++++++++++++++++------
> >>>  2 files changed, 57 insertions(+), 10 deletions(-)
> >>> 
> >>> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> >>> index 9d344da55056..4e0053e64f14 100644
> >>> --- a/drivers/gpu/drm/i915/i915_reg.h
> >>> +++ b/drivers/gpu/drm/i915/i915_reg.h
> >>> @@ -1105,6 +1105,7 @@
> >>>  #define   GMBUS_CYCLE_INDEX	(2<<25)
> >>>  #define   GMBUS_CYCLE_STOP	(4<<25)
> >>>  #define   GMBUS_BYTE_COUNT_SHIFT 16
> >>> +#define   GMBUS_BYTE_COUNT_MAX   256U
> >>>  #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 d1c1e0f7f262..36b720475dc0 100644
> >>> --- a/drivers/gpu/drm/i915/intel_i2c.c
> >>> +++ b/drivers/gpu/drm/i915/intel_i2c.c
> >>> @@ -276,18 +276,17 @@ gmbus_wait_idle(struct drm_i915_private *dev_priv)
> >>>  }
> >>>  
> >>>  static int
> >>> -gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
> >>> -		u32 gmbus1_index)
> >>> +gmbus_xfer_read_chunk(struct drm_i915_private *dev_priv,
> >>> +		      unsigned short addr, u8 *buf, unsigned int len,
> >>> +		      u32 gmbus1_index)
> >>>  {
> >>>  	int reg_offset = dev_priv->gpio_mmio_base;
> >>> -	u16 len = msg->len;
> >>> -	u8 *buf = msg->buf;
> >>>  
> >>>  	I915_WRITE(GMBUS1 + reg_offset,
> >>>  		   gmbus1_index |
> >>>  		   GMBUS_CYCLE_WAIT |
> >>>  		   (len << GMBUS_BYTE_COUNT_SHIFT) |
> >>> -		   (msg->addr << GMBUS_SLAVE_ADDR_SHIFT) |
> >>> +		   (addr << GMBUS_SLAVE_ADDR_SHIFT) |
> >>>  		   GMBUS_SLAVE_READ | GMBUS_SW_RDY);
> >>>  	while (len) {
> >>>  		int ret;
> >>> @@ -309,11 +308,35 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
> >>>  }
> >>>  
> >>>  static int
> >>> -gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
> >>> +gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
> >>> +		u32 gmbus1_index)
> >>>  {
> >>> -	int reg_offset = dev_priv->gpio_mmio_base;
> >>> -	u16 len = msg->len;
> >>>  	u8 *buf = msg->buf;
> >>> +	unsigned int rx_size = msg->len;
> >>> +	unsigned int len;
> >>> +	int ret;
> >>> +
> >>> +	do {
> >>> +		len = min(rx_size, GMBUS_BYTE_COUNT_MAX);
> >>> +
> >>> +		ret = gmbus_xfer_read_chunk(dev_priv, msg->addr,
> >>> +					    buf, len, gmbus1_index);
> >>> +		if (ret)
> >>> +			return ret;
> >>> +
> >>> +		rx_size -= len;
> >>> +		buf += len;
> >>> +	} while (rx_size != 0);
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +
> >>> +static int
> >>> +gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
> >>> +		       unsigned short addr, u8 *buf, unsigned int len)
> >>> +{
> >>> +	int reg_offset = dev_priv->gpio_mmio_base;
> >>> +	unsigned int chunk_size = len;
> >>>  	u32 val, loop;
> >>>  
> >>>  	val = loop = 0;
> >>> @@ -325,8 +348,8 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
> >>>  	I915_WRITE(GMBUS3 + reg_offset, val);
> >>>  	I915_WRITE(GMBUS1 + reg_offset,
> >>>  		   GMBUS_CYCLE_WAIT |
> >>> -		   (msg->len << GMBUS_BYTE_COUNT_SHIFT) |
> >>> -		   (msg->addr << GMBUS_SLAVE_ADDR_SHIFT) |
> >>> +		   (chunk_size << GMBUS_BYTE_COUNT_SHIFT) |
> >>> +		   (addr << GMBUS_SLAVE_ADDR_SHIFT) |
> >>>  		   GMBUS_SLAVE_WRITE | GMBUS_SW_RDY);
> >>>  	while (len) {
> >>>  		int ret;
> >>> @@ -343,6 +366,29 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
> >>>  		if (ret)
> >>>  			return ret;
> >>>  	}
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +
> >>> +static int
> >>> +gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
> >>> +{
> >>> +	u8 *buf = msg->buf;
> >>> +	unsigned int tx_size = msg->len;
> >>> +	unsigned int len;
> >>> +	int ret;
> >>> +
> >>> +	do {
> >>> +		len = min(tx_size, GMBUS_BYTE_COUNT_MAX);
> >>> +
> >>> +		ret = gmbus_xfer_write_chunk(dev_priv, msg->addr, buf, len);
> >>> +		if (ret)
> >>> +			return ret;
> >>> +
> >>> +		buf += len;
> >>> +		tx_size -= len;
> >>> +	} while (tx_size != 0);
> >>> +
> >>>  	return 0;
> >>>  }
> >>>  
> >>> -- 
> >>> 2.3.7
> >>> 
> >>> --
> >>> To unsubscribe from this list: send the line "unsubscribe stable" in
> >>> the body of a message to majordomo@vger.kernel.org
> >>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >
> > -- 
> > Jani Nikula, Intel Open Source Technology Center
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center