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

[Jani Nikula <jani.nikula@intel.com>]

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


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
>> 
>> --
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-- 
Jani Nikula, Intel Open Source Technology Center