RE: [PATCH v4 1/6] can: flexcan: Remodel FlexCAN register r/w APIs for big endian FlexCAN controllers.

[Pankaj Bansal <pankaj.bansal@xxxxxxx>]

> -----Original Message-----
> From: Marc Kleine-Budde [mailto:mkl@xxxxxxxxxxxxxx]
> Sent: Friday, November 24, 2017 8:33 PM
> To: Pankaj Bansal <pankaj.bansal@xxxxxxx>; wg@xxxxxxxxxxxxxx; linux-
> can@xxxxxxxxxxxxxxx; robh+dt@xxxxxxxxxx; mark.rutland@xxxxxxx;
> devicetree@xxxxxxxxxxxxxxx
> Cc: Varun Sethi <V.Sethi@xxxxxxx>; Poonam Aggrwal
> <poonam.aggrwal@xxxxxxx>; Bhupesh Sharma
> <bhupesh.sharma@xxxxxxxxxxxxx>; Sakar Arora
> <Sakar.Arora@xxxxxxxxxxxxx>
> Subject: Re: [PATCH v4 1/6] can: flexcan: Remodel FlexCAN register r/w APIs
> for big endian FlexCAN controllers.
> 
> On 11/24/2017 02:22 PM, Pankaj Bansal wrote:
> > The FlexCAN driver assumed that FlexCAN controller is big endian for
> > powerpc architecture and little endian for other architectures.
> >
> > But this may not be the case. FlexCAN controller can be little or big
> > endian on any architecture. For e.g. NXP LS1021A ARM based SOC has big
> > endian FlexCAN controller.
> >
> > Therefore, the driver has been modified to add a provision for both
> > types of controllers using an additional device tree property. On a
> > "fsl,p1010-flexcan" device BE is default, on all other devices LE is.
> >
> > Big Endian controllers should have "big-endian" set in the device tree.
> > check "Documentation/devicetree/bindings/net/can/fsl-flexcan.txt" for
> > usage.
> >
> > This is the standard practice followed in linux. for more info check:
> > Documentation/devicetree/bindings/common-properties.txt
> >
> > Signed-off-by: Pankaj Bansal <pankaj.bansal@xxxxxxx>
> > Signed-off-by: Bhupesh Sharma <bhupesh.sharma@xxxxxxxxxxxxx>
> > Signed-off-by: Sakar Arora <Sakar.Arora@xxxxxxxxxxxxx>
> > Reviewed-by: Zhengxiong Jin <Jason.Jin@xxxxxxxxxxxxx>
> > Reviewed-by: Poonam Aggrwal <poonam.aggrwal@xxxxxxx>
> > ---
> > Changes in v4:
> >   - Merged device tree changes and driver changes in one series
> > Changes in v3:
> >   - Added fsl,imx25-flexcan, fsl,imx35-flexcan and fsl,imx53-flexcan
> >     support to the driver.
> >   - Modified patch deciption to state default endianness followed and
> >     to include fsl-flexcan.txt referance.
> > Changes in v2:
> >   - Modified patch deciption to include common-properties.txt reference.
> >   - Reorder the LE/BE read/write APIs for better readability of code
> >   - Added an exception to force BE API selection, for powerpc based
> platform
> >     P1010. This ensures that new linux kernel works with old P1010
> >     device-tree, while future powerpc platforms that use big endian
> >     FlexCAN controller need to specify big-endian in device tree in
> >     FlexCAN node.
> >   - Tested on P1010 after backporting to freescale sdk 1.4 linux, without
> >     any change in device-tree.
> >   - Tested on NXP LS1021A arm based platform.
> >
> >  drivers/net/can/flexcan.c | 233 ++++++++++++++++++++----------------
> >  1 file changed, 131 insertions(+), 102 deletions(-)
> >
> > diff --git a/drivers/net/can/flexcan.c b/drivers/net/can/flexcan.c
> > index a13a489..4c873fb 100644
> > --- a/drivers/net/can/flexcan.c
> > +++ b/drivers/net/can/flexcan.c
> 
> [...]
> I think this will select LE for non DT devices, right?
> 

Yes.  As per below code snippet:

static struct property *__of_find_property(const struct device_node *np,
					   const char *name, int *lenp)
{
	struct property *pp;

	if (!np)
		return NULL;
              ....
}

If no device node is present null is returned.
So we select le as default.

> > +	if (of_property_read_bool(pdev->dev.of_node, "big-endian")) {
> > +		priv->read = flexcan_read_be;
> > +		priv->write = flexcan_write_be;
> > +	} else {
> > +		if (of_device_is_compatible(pdev->dev.of_node,
> > +					    "fsl,p1010-flexcan")) {
> > +			priv->read = flexcan_read_be;
> > +			priv->write = flexcan_write_be;
> > +		} else {
> > +			priv->read = flexcan_read_le;
> > +			priv->write = flexcan_write_le;
> > +		}
> > +	}
> > +
> >  	priv->can.clock.freq = clock_freq;
> >  	priv->can.bittiming_const = &flexcan_bittiming_const;
> >  	priv->can.do_set_mode = flexcan_set_mode;
> >
> 
> Marc
> 
> --
> Pengutronix e.K.                  | Marc Kleine-Budde           |
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