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From:   Sagar Shrikant Kadam <sagar.kadam@sifive.com>
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        Sagar Shrikant Kadam <sagar.kadam@sifive.com>
Subject: [PATCH 0/1] fix i2c polling mode workaround for FU540-C000 SoC
Date:   Tue,  6 Oct 2020 10:53:15 -0700
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The polling mode workaround for the FU540-C000 on HiFive Unleashed A00
board was added earlier. The logic for this seems to work only in case
the interrupt property was missing/not added into the i2c0 device node.

Here we address this issue by identifying the SOC based on compatibility
string and set the master xfer's to polling mode if it's the FU540-C000
SoC.

The fix has been tested on Linux 5.9.0-rc8 with a PMOD based RTCC sensor
connected to I2C pins J1 header of the board. Log for reference

# uname -a
Linux buildroot 5.9.0-rc8-00001-gf806864 #2 SMP Tue Oct 6 09:51:24 PDT 2020 riscv64 GNU/Linux
#
# i2cdetect -y 0
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- 57 -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 6f
70: -- -- -- -- -- -- -- --
# i2cget  0 0x57 0 b -y
0xa9
# i2cset  0 0x57 0 0xa5 b -y
# i2cget  0 0x57 0 b -y
0xa5
# i2cset  0 0x57 0 0x5a b -y
# i2cget  0 0x57 0 b -y
0x5a
# i2cget  0 0x6f 0 b -y
0x00
# i2cset  0 0x6f 0 0x5a b -y
# i2cget  0 0x6f 0 b -y
0x5a

Without the fix here, it's observed that "i2cdetect -y 0" turns the 
system unresponsive, with CPU stall messages.

Sagar Shrikant Kadam (1):
  i2c: ocores: fix polling mode workaround on FU540-C000 SoC

 drivers/i2c/busses/i2c-ocores.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

-- 
2.7.4