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Date:   Mon, 22 Apr 2019 15:54:33 +0000
From:   Vitor Soares <Vitor.Soares@...opsys.com>
To:     Boris Brezillon <boris.brezillon@...labora.com>,
        Vitor Soares <Vitor.Soares@...opsys.com>
CC:     "linux-i3c@...ts.infradead.org" <linux-i3c@...ts.infradead.org>,
        "joao.pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/3] i3c: fix i2c and i3c scl rate by bus mode

Hi Boris,

From: Boris Brezillon <boris.brezillon@...labora.com>
Date: Tue, Apr 16, 2019 at 15:52:50

> On Tue, 16 Apr 2019 14:24:57 +0000
> Vitor Soares <vitor.soares@...opsys.com> wrote:
> 
> > Hi Boris,
> > 
> > From: Boris Brezillon <boris.brezillon@...labora.com>
> > Date: Tue, Apr 16, 2019 at 06:50:41
> > 
> > > On Mon, 15 Apr 2019 20:46:41 +0200
> > > Vitor Soares <vitor.soares@...opsys.com> wrote:
> > >   
> > > > Currently in case of mixed slow bus topologie and all i2c devices
> > > > support FM+ speed, the i3c subsystem limite the SCL to FM speed.  
> > >   
> > 
> > I will it replace with your message below.
> > 
> > > "
> > > Currently the I3C framework limits SCL frequency to FM speed when
> > > dealing with a mixed slow bus, even if all I2C devices are FM+ capable.
> > > "
> > >   
> > > > Also in case on mixed slow bus mode the max speed for both
> > > > i2c or i3c transfers is FM or FM+.  
> > > 
> > > Looks like you're basically repeating what you said above.  
> > 
> > What I meant was that I3C framework isn't limiting the I3C speed in case 
> > of mixed slow bus.
> 
> Oh, okay, then maybe something like
> 
> "
> The core was also not accounting for I3C speed limitations when
> operating in mixed slow mode and was erroneously using FM+ speed as the
> max I2C speed when operating in mixed fast mode.
> "

Sounds good to me. Thanks for the advise.

> 
> > 
> > >   
> > > > 
> > > > This patch fix the definition of i2c and i3c scl rate based on bus  
> > > 
> > > 	     ^fixes					      on the bus
> > >   
> > > > topologie and LVR[4] if no user input.  
> > > 
> > >   ^topology		^if the rate is not already specified by the user.
> > >   
> > > > In case of mixed slow mode the i3c scl rate is overridden.  
> > > 
> > > 							   ^ with the max
> > > I2C rate.
> > >   
> > > > 
> > > > Fixes: 3a379bbcea0a ("i3c: Add core I3C infrastructure")
> > > > Signed-off-by: Vitor Soares <vitor.soares@...opsys.com>
> > > > Cc: Boris Brezillon <bbrezillon@...nel.org>
> > > > Cc: <stable@...r.kernel.org>
> > > > Cc: <linux-kernel@...r.kernel.org>
> > > > ---
> > > >  drivers/i3c/master.c | 39 +++++++++++++++++++++++++--------------
> > > >  1 file changed, 25 insertions(+), 14 deletions(-)
> > > > 
> > > > diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> > > > index 909c2ad..1c4a86a 100644
> > > > --- a/drivers/i3c/master.c
> > > > +++ b/drivers/i3c/master.c
> > > > @@ -564,20 +564,30 @@ static const struct device_type i3c_masterdev_type = {
> > > >  	.groups	= i3c_masterdev_groups,
> > > >  };
> > > >  
> > > > -int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode)
> > > > +int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode,
> > > > +		     unsigned long i2c_scl_rate)  
> > > 
> > > 
> > > Can we rename the last arg into max_i2c_scl_rate?  
> > 
> > The i2c_scl_rate is base on LVR[4] bit and the user can set a higher scl 
> > rate, this is reason I didn't named it to max_i2c_scl_rate.
> > But if you think that make more sense I'm ok with that.
> 
> In this context it does encode the maximum rate allowed by the spec
> (based on LVR parsing), so max_i2c_rate sounds like a correct name to
> me.
> 
> > 
> > >   
> > > >  {
> > > >  	i3cbus->mode = mode;
> > > >  
> > > > -	if (!i3cbus->scl_rate.i3c)
> > > > -		i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> > > > -
> > > > -	if (!i3cbus->scl_rate.i2c) {
> > > > -		if (i3cbus->mode == I3C_BUS_MODE_MIXED_SLOW)
> > > > -			i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE;
> > > > -		else
> > > > -			i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_PLUS_SCL_RATE;
> > > > +	switch (i3cbus->mode) {
> > > > +	case I3C_BUS_MODE_PURE:
> > > > +		if (!i3cbus->scl_rate.i3c)
> > > > +			i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> > > > +		break;
> > > > +	case I3C_BUS_MODE_MIXED_FAST:
> > > > +		if (!i3cbus->scl_rate.i3c)
> > > > +			i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> > > > +		if (!i3cbus->scl_rate.i2c)
> > > > +			i3cbus->scl_rate.i2c = i2c_scl_rate;
> > > > +		break;
> > > > +	case I3C_BUS_MODE_MIXED_SLOW:
> > > > +		if (!i3cbus->scl_rate.i2c)
> > > > +			i3cbus->scl_rate.i2c = i2c_scl_rate;
> > > > +		i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c;  
> > > 
> > > Maybe we should do
> > > 
> > > 		if (!i3cbus->scl_rate.i3c ||
> > > 		    i3cbus->scl_rate.i3c > i3cbus->scl_rate.i2c)
> > > 			i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c;
> > > 					   
> > > Just in case the I3C rate forced by the user is lower than the max I2C
> > > rate.  
> > 
> > That was something that I considered but TBH it isn't a real use case.
> 
> Add a WARN_ON() to at least catch such inconsistencies. And maybe we
> should add a dev_warn() when the user-defined rates do not match
> the mode/LVR constraints. It's easy to do a mistake when writing a dts.

I think the WARN_ON() is too evasive on the screen and won't provide the 
information we want.
The dev_warn() should work perfectly here.

		if (i3cbus->scl_rate.i3c < i3cbus->scl_rate.i2c)
			dev_warn(&i3cbus->cur_master->dev->dev,
				     "%s: i3c-scl-hz lower then i2c-scl-hz\n",  __func__);
		if (i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_SCL_RATE ||
		    i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_PLUS_SCL_RATE)
			dev_warn(&i3cbus->cur_master->dev->dev,
				     "%s: i2c-scl-hz not defined according MIPI I3C spec\n", 
				     __func__);

Maybe it make more sense to do this check on of_populate_i3c_bus(), what 
do you think?




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