On Wed, May 27, 2020 at 04:36:56PM +0300, Andy Shevchenko wrote: > On Wed, May 27, 2020 at 03:25:25PM +0300, Serge Semin wrote: > > Recently the I2C-controllers slave interface support was added to the > > kernel I2C subsystem. In this case Linux can be used as, for example, > > a I2C EEPROM machine. See [1] for details. Other than instantiating > > the EEPROM-slave device from user-space there is a way to declare the > > device in dts. In this case firstly the I2C bus controller must support > > the slave interface. Secondly I2C-slave sub-node of that controller > > must have "reg"-property with flag I2C_OWN_SLAVE_ADDRESS set (flag is > > declared in [2]). That flag is declared as (1 << 30), which when set > > makes dtc unhappy about too big address set for a I2C-slave: > > > > Warning (i2c_bus_reg): /example-2/i2c@1120000/eeprom@64: I2C bus unit address format error, expected "40000064" > > Warning (i2c_bus_reg): /example-2/i2c@1120000/eeprom@64:reg: I2C address must be less than 10-bits, got "0x40000064" > > > > Similar problem would have happened if we had set the 10-bit address > > flag I2C_TEN_BIT_ADDRESS in the "reg"-property. > > > > In order to fix the problem we suggest to alter the I2C-bus reg-check > > algorithm, so one would be aware of the upper bits set. Normally if no > > flag specified, the 7-bit address is expected in the "reg"-property. > > If I2C_TEN_BIT_ADDRESS is set, then the 10-bit address check will be > > performed. The I2C_OWN_SLAVE_ADDRESS flag will be just ignored. > > > > [1] kernel/Documentation/i2c/slave-interface.rst > > [2] kernel/include/dt-bindings/i2c/i2c.h > > ... > > > + addr = reg & 0x3FFFFFFFU; > > + if ((reg & (1 << 31)) && addr > 0x3ff) > > FAIL_PROP(c, dti, node, prop, "I2C address must be less than 10-bits, got \"0x%x\"", > > - reg); > > - > > + addr); > > + else if (!(reg & (1 << 31)) && addr > 0x7f) > > + FAIL_PROP(c, dti, node, prop, "I2C address must be less than 7-bits, got \"0x%x\"", > > + addr); > > 1 << 31 is UB. Good point. Thanks. -Sergey > > -- > With Best Regards, > Andy Shevchenko > >
