[U-Boot] [PATCH V2] arm: omap: i2c: don't zero cnt in i2c_write

[Lubomir Popov <lpopov@mm-sol.com>]

Hi Lokesh,

On 03/12/13 06:02, Lokesh Vutla wrote:
> Hi Lubomir,
> On Monday 02 December 2013 09:17 PM, Lubomir Popov wrote:
>> Hi Nikita,
>>
>> On 28/11/13 18:04, Nikita Kiryanov wrote:
>>> Writing zero into I2Ci.I2C_CNT register causes random I2C failures in OMAP3
>>> based devices. This seems to be related to the following advisory which
>>> apears in multiple erratas for OMAP3 SoCs (OMAP35xx, DM37xx), as well as
>>> OMAP4430 TRM:
>>>
>>> Advisory:
>>> I2C Module Does Not Allow 0-Byte Data Requests
>>> Details:
>>> When configured as the master, the I2C module does not allow 0-byte data
>>> transfers. Note: Programming I2Ci.I2C_CNT[15:0]: DCOUNT = 0 will cause
>>> undefined behavior.
>>> Workaround(s):
>>> No workaround. Do not use 0-byte data requests.
>>>
>>> The writes in question are unnecessary from a functional point of view.
>>> Most of them are done after I/O has finished, and the only one that preceds
>>> I/O (in i2c_probe()) is also unnecessary because a stop bit is sent before
>>> actual data transmission takes place.
>>>
>>> Therefore, remove all writes that zero the cnt register.
>>>
>>> Cc: Heiko Schocher <hs@denx.de>
>>> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
>>> Cc: Tom Rini <trini@ti.com>
>>> Cc: Lubomir Popov <lpopov@mm-sol.com>
>>> Cc: Enric Balletbo Serra <eballetbo@gmail.com>
>>> Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
>>> ---
>>> Changes in V2:
>>>      Removed all instances of writew(0, &i2c_base->cnt) instead of just the
>>>      one in i2c_write (following a test of V1 by Thomas Petazzoni).
>>>
>>>
>> Tested-by: Lubomir Popov <lpopov@mm-sol.com>
>>
>> In addition to the OMAP5430/32 tests performed last week, tested today
>> on OMAP4 (4430/60/70) and on AM3359. Thus tests have covered OMAP4/5-
>> compatible I2C IPs with revnb_lo=[0x000a to 0x000c] (revnb_hi is 0x5040
>> for all those IPs).
> May I know on top of which tree,tag you are trying this patch ?
> I tried OMAP4 on top of v2014.01-rc1, but I am not able to boot. I applied this patch and still
> not able to boot. There is a mail thread going on, on this topic.
> So I just wanted to know that I am not missing very obvious.
For most boards (the OMAP5432 uEVM, our OMAP5430 board, the 4460 Pandaboard ES, the
AM335x General Purpose EVM and the AM335x Starter Kit) this was a version of the 
master
branch that I cloned on Nov. 12. See dump below (with some debug prints added to 
display
the I2C core revision numbers):

U-Boot SPL 2013.10-00339-gd7adce9-dirty (Dec 03 2013 - 09:31:33)
OMAP5432 ES2.0
SPL: Please implement spl_start_uboot() for your board
SPL: Direct Linux boot not active!
reading u-boot.img
reading u-boot.img


U-Boot 2013.10-00339-gd7adce9-dirty (Dec 03 2013 - 09:31:33)

CPU  : OMAP5432 ES2.0
Board: OMAP5432 uEVM
I2C:   I2C_REVNB_LO: 0x0000000c
I2C_REVNB_HI: 0x00005040
ready
DRAM:  2 GiB
I2C_REVNB_LO: 0x0000000c
I2C_REVNB_HI: 0x00005040
I2C_REVNB_LO: 0x0000000c
I2C_REVNB_HI: 0x00005040
MMC:   OMAP SD/MMC: 0, OMAP SD/MMC: 1
Using default environment

I2C_REVNB_LO: 0x0000000c
I2C_REVNB_HI: 0x00005040
Net:   No ethernet found.
Hit any key to stop autoboot:  0
U-Boot#

For our OMAP4 board (on which I tested the OMAP4430 ES2.1, OMAP4460 ES1.0 and ES1.1,
and OMAP4470 ES1.0, by means of TI Blaze/Tablet processor cards) I used a 2013.04
version of U-Boot, on which I developed the new I2C driver back then and on which
the submitted driver patches were based (the driver was mainlined in 2013.07, 
AFAIR);
in this version I also have working support for OMAP4470/TWL6032 (not mainlined). I
did so because the 2013.10 version used for the other boards won't boot on our 
OMAP4,
and I didn't have time to investigate why (it did boot on the Panda ES though).

The reason to not use the current master branch is ridiculous - my workplace is for
some months now within the TI intranet, and since about mid November, when some 
network
infrastructure reorg happened, the TI proxy blocks my access to any git repo. 
Because
my current work is not related to software, I haven't actively opted for 
granting access
until yesterday, and am now waiting.

In summary, what I have done is essentially to confirm that removing all writes of a
0-byte length to the i2c_cnt register (which is _needed_ to fix the OMAP3 
problem) does
not affect operation on OMAP4/5-compatible I2C IPs. I have not applied Nikita's 
fix as
a patch, but have manually commented out those lines in both U-Boot versions 
used for
the test. This is probably against the formal rules, but I stand behind the 
statement
that functionally all is OK.

On which board did you fail to boot OMAP4? Isn't this a strange coincidence, aren't
we having a regression...? :-(

-- 
Regards,
Lubo