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    SubjectRe: [PATCHv2 1/3] mfd: add STMPE I/O Expander support
    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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