Messages in this thread |  | | | Date | Tue, 29 Jun 2010 08:43:26 +0530 | | From | Rabin VINCENT <> | | Subject | Re: [PATCHv2 1/3] mfd: add STMPE I/O Expander support |
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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?
> What I suggest is that you'd have the exported routines taking your stmpe > lock, and then have an internal version (e.g. named with a __stmpe prefix) > without lock taken for your core code. In your case, you could probably call > the i2c I/O routines directly, that's up to you. > > > +/** > > + * stmpe_set_bits() - set the value of a bitfield in a stmpe register > > + * @stmpe: device to write to > > + * @reg: register to write > > + * @mask: mask of bits to set > > + * @val: value to set > > + */ > > +int stmpe_set_bits(struct stmpe *stmpe, u8 reg, u8 mask, u8 val) > > +{ > > + int ret; > > + > > + mutex_lock(&stmpe->lock); > > + > > + ret = stmpe_reg_read(stmpe, reg); > That one for example would be __stmpe_read(). > > > +/** > > + * 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. I'll fix it as your recommended, though. Will fix your other comments too.
Rabin
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