On Mon, Oct 21, 2019 at 06:41:05PM +0300, Andi Shyti wrote:

Hi Stephan,

quoted

Not sure if you saw my comment regarding your patch [1],
so I'll just repeat it properly inline here:

[1]: https://patchwork.kernel.org/patch/11178515/#22927311

On Sun, Oct 20, 2019 at 11:28:55PM +0300, Andi Shyti wrote:

quoted

The exchange of data to and from the mms114 touchscreen never
exceeds 256 bytes. In the worst case it goes up to 80 bytes in
the interrupt handler while reading the events.

i2c_smbus_read_i2c_block_data() is actually limited to
I2C_SMBUS_BLOCK_MAX = 32.

oh sorry, I don't know how I slipped on this.

But this means that the i2c in the kernel is wrong (or outdated),
smbus specifies 256 bytes of data[*]. I might have relied on the
specification more than the code.

I guess SMBUS needs some update.

You are right. It seems like that part of the specification was changed
with SMBus version 3.0 [1]:

  D.6 255 Bytes in Process Call:
    The maximum number of bytes allowed in the Block Write-Block Read
    Process Call (Section 6.5.8) was increased from 32 to 255.

[1]: http://www.smbus.org/specs/SMBus_3_0_20141220.pdf