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Message-ID: <20091104222839.GA15988@pengutronix.de>
Date: Wed, 4 Nov 2009 23:28:39 +0100
From: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>
To: Samuel Ortiz <sameo@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org,
Sascha Hauer <s.hauer@...gutronix.de>,
Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [PATCH] mfd/mc13783: near complete rewrite
Hello Samuel,
On Wed, Nov 04, 2009 at 07:35:08PM +0100, Samuel Ortiz wrote:
> > - * Copyright 2009 Pengutronix, Sascha Hauer <s.hauer@...gutronix.de>
> Even though this looks like a major rewrite, I still think it's unfair to
> remove Sascha from there.
OK.
> > +void mc13783_lock(struct mc13783 *mc13783)
> > +{
> > + if (!mutex_trylock(&mc13783->lock)) {
> > + dev_dbg(&mc13783->spidev->dev, "wait for %s from %pf\n",
> > + __func__, __builtin_return_address(0));
> > +
> > + mutex_lock(&mc13783->lock);
> That is just for debugging purposes, right ?
Yes, the intention is to see lock contentions. I thought about making
this
#if defined(DEBUG)
if (!mutex_trylock(&mc13783->lock)) {
...
}
dev_dbg(...)
#else
mutex_lock(...);
#endif
but it didn't feel right to have a different locking scheme depending on
DEBUG or not. Does your question imply that I should change something
here?
> > +static int mc13783_prep_read_transfer(struct mc13783 *mc13783,
> > + struct spi_transfer *t, u32 *buf,
> > + unsigned int offset, u32 *val
> What is val used for in that function ?
It's there for symmetry with mc13783_eval_read_transfer.
> )
> > +{
> > + if (offset > MC13783_NUMREGS)
> > return -EINVAL;
> > - return len - m.actual_length;
> > +
> > + buf[0] = offset << 25;
> Could we have a define for that 25 ?
Yes, will do.
> > + memset(t, 0, sizeof(*t));
> > +
> > + t->tx_buf = buf;
> > + t->rx_buf = buf;
> > + t->len = sizeof(u32);
> > +
> > + return 1;
> > }
> >
> > -static int mc13783_read(struct mc13783 *mc13783, int reg_num, u32 *reg_val)
> > +static int mc13783_eval_read_transfer(struct mc13783 *mc13783,
> > + struct spi_transfer *t, u32 *buf,
> > + unsigned int offset, u32 *val)
> > {
> > - unsigned int frame = 0;
> > - int ret = 0;
> > + BUG_ON(t->tx_buf != buf || t->rx_buf != buf);
> your SPI read will be on t->rx_buf. I could understand that you want to check
> for t->rx_buf not being NULL (although a BUG_ON() seems too much here), but
> checking for t->rx_buf pointing to buf really looks akward to me.
The intention here is to assert that mc13783_eval_read_transfer is
called for a transfer prepared by mc13783_prep_read_transfer. As this
sets up t->tx_buf = t->rx_buf = buf, it seems to be the right assertion.
> why not:
>
> BUG_ON(t->rx_buf == NULL)
>
> *val = *((u32 *)t->rx_buf) & 0xffffff;
>
> > -static int mc13783_write(struct mc13783 *mc13783, int reg_num, u32 reg_val)
> > +static int mc13783_eval_write_transfer(struct mc13783 *mc13783,
> > + struct spi_transfer *t, u32 *buf,
> > + unsigned int offset, u32 val)
> > {
> > - unsigned int frame = 0;
> > + BUG_ON(t->tx_buf != buf || t->rx_buf != buf);
> >
> > - if (reg_num > MC13783_MAX_REG_NUM)
> > - return -EINVAL;
> > + return 1;
> > +}
> I dont get the point of mc13783_eval_write_transfer().
The idea here is that I could setup, send and receive multi-transfer
messages with a single buffer array. Then the return value would tell me how
much to advance in the buffer for the next result. Maybe that's just
paranoid over-engineering.
> > +int mc13783_reg_read(struct mc13783 *mc13783, unsigned int offset, u32 *val)
> > +{
> > + u32 buf;
> > + struct spi_transfer t;
> > + struct spi_message m;
> > + int ret;
> > +
> > + BUG_ON(!mutex_is_locked(&mc13783->lock));
> > +
> > + ret = mc13783_prep_read_transfer(mc13783, &t, &buf, offset, val);
> Do you really need buf here ?
> I think mc13783_prep_read_transfer(mc13783, &t, val, offset); should be
> enough.
Yes, should work.
> > + if (ret < 0)
> > + return ret;
> > +
> > + spi_message_init(&m);
> > + spi_message_add_tail(&t, &m);
> > +
> > + ret = spi_sync(mc13783->spidev, &m);
> >
> > - frame |= (1 << MC13783_WRITE_BIT_SHIFT);
> > - frame |= reg_num << MC13783_REG_NUM_SHIFT;
> > - frame |= reg_val & MC13783_FRAME_MASK;
> > + /* error in message.status implies error return from spi_sync */
> > + BUG_ON(!ret && m.status);
> So, you really want to crash your board because of an SPI inconsistency ?
> Seems like an overkill to me.
This only bugs if spi_sync succeeds even though the message wasn't
transfered correctly. Sascha's driver had:
if (spi_sync(spi, &m) != 0 || m.status != 0)
return -EINVAL;
If I understand spi_sync correctly m.status != 0 implies spi_sync
returning != 0, so the above should be equivalent to:
if (spi_sync(spi, &m) != 0)
return -EINVAL;
So my BUG_ON is only for the case that Sascha saw something I missed.
> > + ret = mc13783_eval_write_transfer(mc13783, &t, &buf, offset, val);
> Again, I dont see the point of this function.
Do you insist on fixing that? It might look a bit strange (which is
subjective) but I don't see much benefit in changing it because I expect
the compiler to produce similar code. Currently all
mc13783_{prep,eval}_{read,write}_transfer calls are inlined by my
compiler anyhow.
Best regards and thanks for your comments,
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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