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From: Boris Brezillon <boris.brezillon@collabora.com>
To: Vitor Soares <Vitor.Soares@synopsys.com>
Cc: "linux-i3c@lists.infradead.org" <linux-i3c@lists.infradead.org>,
	"joao.pinto@synopsys.com" <Joao.Pinto@synopsys.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>,
	Boris Brezillon <bbrezillon@kernel.org>
Subject: Re: [PATCH 1/3] i3c: fix i2c and i3c scl rate by bus mode
Date: Mon, 22 Apr 2019 18:07:15 +0200
Message-ID: <20190422180715.40abe1b9@collabora.com> (raw)
In-Reply-To: <13D59CF9CEBAF94592A12E8AE55501350A61B3B4@DE02WEMBXB.internal.synopsys.com>

On Mon, 22 Apr 2019 15:54:33 +0000
Vitor Soares <Vitor.Soares@synopsys.com> wrote:


> > > >     
> > > > >  {
> > > > >  	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__);

Using dev_warn() sounds good, though I don't think you need the
__func__ here. Also, please print the i2c/i3c rates in the message, and
align the second line on the open parens.

> 		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__);

Is that really a problem? Having an i2c rate that is less than FM speed
sounds like a valid case to me.

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

No, we really want to have this check here, because we might support
other HW description formats at some point (board-files, ACPI, ...).

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Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-15 18:46 [PATCH 0/3] Fix i2c and i3c scl rate according " Vitor Soares
2019-04-15 18:46 ` [PATCH 1/3] i3c: fix i2c and i3c scl rate by " Vitor Soares
2019-04-16  5:50   ` Boris Brezillon
2019-04-16 14:24     ` Vitor Soares
2019-04-16 14:52       ` Boris Brezillon
2019-04-22 15:54         ` Vitor Soares
2019-04-22 16:07           ` Boris Brezillon [this message]
2019-04-22 17:54             ` Vitor Soares
2019-04-22 18:27               ` Boris Brezillon
2019-04-22 19:59                 ` Vitor Soares
2019-04-15 18:46 ` [PATCH 2/3] i3c: add mixed limited " Vitor Soares
2019-04-16  6:00   ` Boris Brezillon
2019-04-16 14:27     ` Vitor Soares
2019-04-15 18:46 ` [PATCH 3/3] i3c: dw: Add limited bus mode support Vitor Soares
2019-04-16  6:09   ` Boris Brezillon

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