Re: [RFC 7/7] [media] rc: add support for IR LEDs driven through SPI
From: Andi Shyti
Date: Thu Jul 21 2016 - 10:57:31 EST
> > > > + ret = regulator_enable(idata->regulator);
> > > > + if (ret)
> > > > + return ret;
> > > > +
> > > > + mutex_lock(&idata->mutex);
> > > > + idata->xfer.len = n;
> > > > + idata->xfer.tx_buf = buffer;
> > > > + mutex_unlock(&idata->mutex);
> > >
> > > I'm not convinced the locking works here. You want to guard against
> > > someone modifying xfer while you are sending (so in spi_sync_transfer),
> > > which this locking is not doing. You could declare a
> > > local "struct spi_transfer xfer" and avoid the mutex altogether.
> > I cannot declare xfer locally because the spi framework needs
> > a statically allocated xfer, so that either I dynamically
> > allocate it in the function or I declare it global in idata.
> It can be stack allocated for sync transfers. You might want to lock
> the spi bus.
no, actually it's just dirty data and laziness, a memset to 0
fixes it :)
> > With the mutex I would like to prevent different tasks to change
> > the value at the same time, it's an easy case, it shouldn't make
> > much difference.
> That's cargo-cult locking. It does not achieve anything.
yes, as I said, it's not a big thing, I can remove the mutex.