linux-kernel - Re: [PATCH v2 4/5] spi: Add OF binding support for SPI busses

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Message-ID: <20080704041758.GH12945@secretlab.ca>
Date:	Thu, 3 Jul 2008 22:17:58 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Chen Gong <G.Chen@...escale.com>
Cc:	david-b@...bell.net, fabrizio.garetto@...il.com,
	linuxppc-dev@...abs.org, spi-devel-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/5] spi: Add OF binding support for SPI busses

On Fri, Jul 04, 2008 at 11:54:57AM +0800, Chen Gong wrote:
> Grant Likely wrote:
> > +		/* Mode (clock phase/polarity/etc.) */
> > +		if (of_find_property(nc, "spi,cpha", NULL))
> > +			spi->mode |= SPI_CPHA;
> > +		if (of_find_property(nc, "spi,cpol", NULL))
> > +			spi->mode |= SPI_CPOL;
> 
> so becuase in function spi_alloc_deive, spi is allocated by kzalloc,
> how about writing as follows:
> 		/* Mode (clock phase/polarity/etc.) */
> 		prop = of_get_property(nc, "spi,cpha", NULL))
>                         if (prop)
> 			spi->mode |= *prop;
> 		prop = of_get_property(nc, "spi,cpol", NULL))
>                         if (prop)
> 			spi->mode |= *prop;

spi,cpha and spi,cpol are defined as empty properties.  The presence of
the property in the node means I need to set the flag in the spi_device.

> > +		/* Select device driver */
> > +		sprop = of_get_property(nc, "linux,modalias", &len);
> > +		if (sprop && len > 0)
> > +			strncpy(spi->modalias, sprop, KOBJ_NAME_LEN);
> > +		else
> > +			strncpy(spi->modalias, "spidev", KOBJ_NAME_LEN);
> > +
>  how about writing as follows:
> 
> 		if (sprop && len > 0)
> 			strncpy(spi->modalias, sprop, KOBJ_NAME_LEN -
> 1);
> 		else
> 			strncpy(spi->modalias, "spidev", KOBJ_NAME_LEN -
> 1);

Actually, neither are very good.  What it should really be is:

	if (sprop && len > 0)
		strlcpy(spi->modalias, sprop, sizeof (spi->modalias));
	else
		strlcpy(spi->modalias, "spidev", sizeof (spi->modalias));

This ensures that the string is always null terminated and always the
right size.

... But the whole argument is a bit moot.  The fact that I even defined
a "linux,modalias" property is a great big hairy hack that I would
never want my mother to see.  Instead, I need a method to bind to an SPI
driver based on the compatible list.  Jon Smirl has done some work
in this regard for i2c, but I haven't looked at it very deeply, and so
do not at all understand it (yet).

Thanks for the comments.
g.
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