linux-kernel - RE: [PATCH 1/3] i3c: fix i2c and i3c scl rate by bus mode

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Date:   Tue, 16 Apr 2019 14:24:57 +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 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.

> 
> > 
> > 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.

> 
> >  {
> >  	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.

> 
> The patch looks good otherwise.

Thanks.

> 
> > +		break;
> > +	default:
> > +		return -EINVAL;
> >  	}
> > -
> >  	/*
> >  	 * I3C/I2C frequency may have been overridden, check that user-provided
> >  	 * values are not exceeding max possible frequency.
> > @@ -1980,9 +1990,6 @@ of_i3c_master_add_i2c_boardinfo(struct i3c_master_controller *master,
> >  	/* LVR is encoded in reg[2]. */
> >  	boardinfo->lvr = reg[2];
> >  
> > -	if (boardinfo->lvr & I3C_LVR_I2C_FM_MODE)
> > -		master->bus.scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE;
> > -
> >  	list_add_tail(&boardinfo->node, &master->boardinfo.i2c);
> >  	of_node_get(node);
> >  
> > @@ -2432,6 +2439,7 @@ int i3c_master_register(struct i3c_master_controller *master,
> >  			const struct i3c_master_controller_ops *ops,
> >  			bool secondary)
> >  {
> > +	unsigned long i2c_scl_rate = I3C_BUS_I2C_FM_PLUS_SCL_RATE;
> >  	struct i3c_bus *i3cbus = i3c_master_get_bus(master);
> >  	enum i3c_bus_mode mode = I3C_BUS_MODE_PURE;
> >  	struct i2c_dev_boardinfo *i2cbi;
> > @@ -2481,9 +2489,12 @@ int i3c_master_register(struct i3c_master_controller *master,
> >  			ret = -EINVAL;
> >  			goto err_put_dev;
> >  		}
> > +
> > +		if (i2cbi->lvr & I3C_LVR_I2C_FM_MODE)
> > +			i2c_scl_rate = I3C_BUS_I2C_FM_SCL_RATE;
> >  	}
> >  
> > -	ret = i3c_bus_set_mode(i3cbus, mode);
> > +	ret = i3c_bus_set_mode(i3cbus, mode, i2c_scl_rate);
> >  	if (ret)
> >  		goto err_put_dev;
> >  

Best regards,
Vitor Soares