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

Jae Hyun Yoo
2018-11-01T18:09:24Z

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
>
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