Re: [PATCH] si2168: use i2c controlled mux interface

[Antti Palosaari <crope@xxxxxx>]

Moikka!

On 01/06/2016 09:14 AM, Peter Rosin wrote:
> Hi Antti,
>
> On 2016-01-06 06:42, Antti Palosaari wrote:
> > Recent i2c mux locking update offers support for i2c controlled i2c
> > muxes. Use it and get the rid of homemade hackish i2c adapter
> > locking code.
>
> That looks good on a first glance, and I'm sure it felt good to get rid
> of the locking workaround :-)

And I forgot mutext to protect si2168_cmd_execute()...

> However, is this safe? From looking at the short datasheet of the si2168,
> it seems that the mux is used to open up the channel to the tuner? But
> what happens is there are two parallel accesses, one to the tuner and one
> to the si2168 chip? With your change, it could happen that the access to
> the si2168 happens while the gate to the tuner is open. Can that break
> anything?
>
> I.e.
>          thread one                      thread two
>          ----------                      ----------
> 	open gate
>                                          access si2168
>          access tuner
>          close gate
>
> If that is safe, then I don't understand why the gate isn't left open
> at all times? The short datasheet is too short to answer my questions...

It is often called I2C Gate or repeater, and yes it is there to block 
noise traveling to tuner. I think that noise could be unnecessary I2C 
traffic as well some digital noise travelling via I2C wires. Tuners are 
usually build using pure digital logic + analog circuits (RF mixers, RF 
filters, RF amplifiers). Leaving gate open usually does not harm and 
there is even some designs it is connected directly to main bus (but 
almost all demodulators still has that kind of gate to connect tuner).

All in all, I don't see it very big issue if only few unwanted I2C 
messages are sent to bus tuner is connected.

> Also, my series needs some Tested-by (and Reviewed-by for that matter),
> and I assume that you have tested it? Is it ok to add something like
> that from you? I understand that you may only be able to test your
> corner of the series, but that would still be very helpful. Thanks!

Yes it worked, but I haven't examined it care enough yet.

However, I think I see one problem: i2c muxes that deselects channel 
automatically, usually after the first i2c stop (P) condition is seen.

regards
Antti

> Cheers,
> Peter
>
> > Cc: Peter Rosin <peda@xxxxxxxxxx>
> > Cc: Peter Rosin <peda@xxxxxxxxxxxxxx>
> > Signed-off-by: Antti Palosaari <crope@xxxxxx>
> > ---
> >   drivers/media/dvb-frontends/si2168.c | 61 ++++--------------------------------
> >   1 file changed, 6 insertions(+), 55 deletions(-)
> >
> > diff --git a/drivers/media/dvb-frontends/si2168.c b/drivers/media/dvb-frontends/si2168.c
> > index ae217b5..d2a5608 100644
> > --- a/drivers/media/dvb-frontends/si2168.c
> > +++ b/drivers/media/dvb-frontends/si2168.c
> > @@ -18,48 +18,15 @@
> >
> >   static const struct dvb_frontend_ops si2168_ops;
> >
> > -/* Own I2C adapter locking is needed because of I2C gate logic. */
> > -static int si2168_i2c_master_send_unlocked(const struct i2c_client *client,
> > -					   const char *buf, int count)
> > -{
> > -	int ret;
> > -	struct i2c_msg msg = {
> > -		.addr = client->addr,
> > -		.flags = 0,
> > -		.len = count,
> > -		.buf = (char *)buf,
> > -	};
> > -
> > -	ret = __i2c_transfer(client->adapter, &msg, 1);
> > -	return (ret == 1) ? count : ret;
> > -}
> > -
> > -static int si2168_i2c_master_recv_unlocked(const struct i2c_client *client,
> > -					   char *buf, int count)
> > -{
> > -	int ret;
> > -	struct i2c_msg msg = {
> > -		.addr = client->addr,
> > -		.flags = I2C_M_RD,
> > -		.len = count,
> > -		.buf = buf,
> > -	};
> > -
> > -	ret = __i2c_transfer(client->adapter, &msg, 1);
> > -	return (ret == 1) ? count : ret;
> > -}
> > -
> >   /* execute firmware command */
> > -static int si2168_cmd_execute_unlocked(struct i2c_client *client,
> > -				       struct si2168_cmd *cmd)
> > +static int si2168_cmd_execute(struct i2c_client *client, struct si2168_cmd *cmd)
> >   {
> >   	int ret;
> >   	unsigned long timeout;
> >
> >   	if (cmd->wlen) {
> >   		/* write cmd and args for firmware */
> > -		ret = si2168_i2c_master_send_unlocked(client, cmd->args,
> > -						      cmd->wlen);
> > +		ret = i2c_master_send(client, cmd->args, cmd->wlen);
> >   		if (ret < 0) {
> >   			goto err;
> >   		} else if (ret != cmd->wlen) {
> > @@ -73,8 +40,7 @@ static int si2168_cmd_execute_unlocked(struct i2c_client *client,
> >   		#define TIMEOUT 70
> >   		timeout = jiffies + msecs_to_jiffies(TIMEOUT);
> >   		while (!time_after(jiffies, timeout)) {
> > -			ret = si2168_i2c_master_recv_unlocked(client, cmd->args,
> > -							      cmd->rlen);
> > +			ret = i2c_master_recv(client, cmd->args, cmd->rlen);
> >   			if (ret < 0) {
> >   				goto err;
> >   			} else if (ret != cmd->rlen) {
> > @@ -109,17 +75,6 @@ err:
> >   	return ret;
> >   }
> >
> > -static int si2168_cmd_execute(struct i2c_client *client, struct si2168_cmd *cmd)
> > -{
> > -	int ret;
> > -
> > -	i2c_lock_adapter(client->adapter);
> > -	ret = si2168_cmd_execute_unlocked(client, cmd);
> > -	i2c_unlock_adapter(client->adapter);
> > -
> > -	return ret;
> > -}
> > -
> >   static int si2168_read_status(struct dvb_frontend *fe, enum fe_status *status)
> >   {
> >   	struct i2c_client *client = fe->demodulator_priv;
> > @@ -610,11 +565,6 @@ static int si2168_get_tune_settings(struct dvb_frontend *fe,
> >   	return 0;
> >   }
> >
> > -/*
> > - * I2C gate logic
> > - * We must use unlocked I2C I/O because I2C adapter lock is already taken
> > - * by the caller (usually tuner driver).
> > - */
> >   static int si2168_select(struct i2c_mux_core *muxc, u32 chan)
> >   {
> >   	struct i2c_client *client = i2c_mux_priv(muxc);
> > @@ -625,7 +575,7 @@ static int si2168_select(struct i2c_mux_core *muxc, u32 chan)
> >   	memcpy(cmd.args, "\xc0\x0d\x01", 3);
> >   	cmd.wlen = 3;
> >   	cmd.rlen = 0;
> > -	ret = si2168_cmd_execute_unlocked(client, &cmd);
> > +	ret = si2168_cmd_execute(client, &cmd);
> >   	if (ret)
> >   		goto err;
> >
> > @@ -645,7 +595,7 @@ static int si2168_deselect(struct i2c_mux_core *muxc, u32 chan)
> >   	memcpy(cmd.args, "\xc0\x0d\x00", 3);
> >   	cmd.wlen = 3;
> >   	cmd.rlen = 0;
> > -	ret = si2168_cmd_execute_unlocked(client, &cmd);
> > +	ret = si2168_cmd_execute(client, &cmd);
> >   	if (ret)
> >   		goto err;
> >
> > @@ -717,6 +667,7 @@ static int si2168_probe(struct i2c_client *client,
> >   	dev->muxc->parent = client->adapter;
> >   	dev->muxc->select = si2168_select;
> >   	dev->muxc->deselect = si2168_deselect;
> > +	dev->muxc->i2c_controlled = true;
> >
> >   	/* create mux i2c adapter for tuner */
> >   	ret = i2c_add_mux_adapter(dev->muxc, 0, 0, 0);

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