Messages in this thread | | | Date | Tue, 29 Jun 2010 17:33:27 +0200 | From | Samuel Ortiz <> | Subject | Re: [PATCHv2 1/3] mfd: add STMPE I/O Expander support |
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Hi Rabin,
On Tue, Jun 29, 2010 at 08:43:26AM +0530, Rabin VINCENT wrote: > Hi Samuel, > > On Mon, Jun 28, 2010 at 01:55:16 +0200, Samuel Ortiz wrote: > > On Tue, Jun 22, 2010 at 07:25:27PM +0530, Rabin Vincent wrote: > > > +int stmpe_reg_read(struct stmpe *stmpe, u8 reg) > > > +{ > > > + int ret; > > > + > > > + ret = i2c_smbus_read_byte_data(stmpe->i2c, reg); > > > + if (ret < 0) > > > + dev_err(stmpe->dev, "failed to read reg %#x: %d\n", > > > + reg, ret); > > > + > > > + dev_vdbg(stmpe->dev, "rd: reg %#x => data %#x\n", reg, ret); > > > + > > > + return ret; > > > +} > > > +EXPORT_SYMBOL(stmpe_reg_read); > > I think your locking is broken here. > > If your exporting this routine (and the next ones below), you'd better make > > sure you're under stmpe->lock for the stmpe register concurrent access. > > stmpe_reg_read() and stmpe_reg_write() are just a call to one > i2c_smbus_* function, and the I2C core takes a bus_lock internally > preventing concurrent accesses. > > The only place where the I2C core locking is not sufficient is the > read/modify/write sequence, and we provide stmpe_set_bits() for that, > which takes a lock. If someone uses reg_read()/reg_write() sequences on > registers where they should be using set_bits(), adding extra locking in > reg_read()/reg_write() will not provide any additional safeguard. > > The same scheme is used by adp5520. > > Could you please explain why more locking is needed? Without the extra locking, there's nothing preventing me from writing to a register while you're in the middle of a stmpe_set_bits() call.
> > > +/** > > > + * stmpe_block_write() - write multiple stmpe registers > > > + * @stmpe: device to write to > > > + * @reg: first register > > > + * @length: number of registers > > > + * @values: values to write > > > + */ > > > +int stmpe_block_write(struct stmpe *stmpe, u8 reg, u8 length, > > > + const u8 *values) > > > +{ > > > + int ret; > > > + > > > + dev_vdbg(stmpe->dev, "wr: regs %#x (%d)\n", reg, length); > > > +#ifdef VERBOSE_DEBUG > > > + print_hex_dump_bytes("stmpe wr: ", dump_prefix_offset, values, length); > > > +#endif > > I don't really enjoy this part for 2 reasons: > > - You should use a less generic ifdef switch, prefixed with STMPE_ for > > example. > > The dev_vdbg() in the previous line is activated via VERBOSE_DEBUG, so > the idea was to have this dump use the same config. Ah, I didnt realize VERBOSE_DEBUG was defined from device.h. Should have grepped for it in your patch, sorry. I would still like it to be part of your header file though.
> I'll fix it as your recommended, though. Will fix your other comments too. Thanks in advance.
Cheers, Samuel.
> Rabin
-- Intel Open Source Technology Centre http://oss.intel.com/
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