Re: [PATCH i2c-next v9 5/5] i2c: aspeed: Add bus idle waiting logic for multi-master use cases

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On 11/1/2018 10:44 AM, kbuild test robot wrote:
Hi Jae,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on wsa/i2c/for-next]
[also build test WARNING on v4.19 next-20181101]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Jae-Hyun-Yoo/dt-bindings-i2c-Add-bus-timeout-ms-and-retries-properties-as-common-optional/20181031-051152
base:   https://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git i2c/for-next
config: i386-allyesconfig (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
         # save the attached .config to linux build tree
         make ARCH=i386

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

    drivers/i2c/busses/i2c-aspeed.c: In function 'aspeed_i2c_master_xfer':
drivers/i2c/busses/i2c-aspeed.c:624:210: warning: 'timeout' may be used uninitialized in this function [-Wmaybe-uninitialized]
       if (time_after(jiffies, timeout))
                                                                                                                                                                                                                      ^
    drivers/i2c/busses/i2c-aspeed.c:607:16: note: 'timeout' was declared here
      unsigned long timeout;
                    ^~~~~~~

vim +/timeout +624 drivers/i2c/busses/i2c-aspeed.c

    604	
    605	static int aspeed_i2c_check_bus_busy(struct aspeed_i2c_bus *bus)
    606	{
    607		unsigned long timeout;
    608	
    609		if (bus->multi_master) {
    610			might_sleep();
    611			/* Initialize it only when multi_master is set */
    612			timeout = jiffies + bus->adap.timeout;

The 'timeout' variable will be initialized only when bus->multi_master
is true to save some OPs in case this variable isn't used. The saved OPs
are not expensive but it makes a meaning because this function is called
very frequently on every master transfer.

    613		}
    614	
    615		for (;;) {
    616			if (!(readl(bus->base + ASPEED_I2C_CMD_REG) &
    617			      ASPEED_I2CD_BUS_BUSY_STS))
    618	#if IS_ENABLED(CONFIG_I2C_SLAVE)
    619				if (bus->slave_state == ASPEED_I2C_SLAVE_STOP)
    620	#endif
    621					return 0;
    622			if (!bus->multi_master)
    623				break;

If bus->multi_master is false then it doesn't fall through so the
'timeout' variable in below will not be used when itself is
uninitialized. Also, bus->multi_master is fixed at probing time and it
doesn't change at runtime so the warning case never happens.

-Jae

  > 624			if (time_after(jiffies, timeout))
    625				break;
    626			usleep_range((ASPEED_I2C_BUS_BUSY_CHECK_INTERVAL_US >> 2) + 1,
    627				     ASPEED_I2C_BUS_BUSY_CHECK_INTERVAL_US);
    628		}
    629	
    630		return aspeed_i2c_recover_bus(bus);
    631	}
    632	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation




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