On Thu, 23 Jul 2015 10:13:11 +0100
Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> On Thu, 23 Jul 2015, Boris Brezillon wrote:
>
> > Hi Lee,
> >
> > On Thu, 23 Jul 2015 08:32:17 +0100
> > Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> >
> > > On Wed, 22 Jul 2015, Cyrille Pitchen wrote:
> > > > + for_each_child_of_node(np, child) {
> > > > + const char *compatible;
> > > > + int cplen;
> > > > +
> > > > + if (!of_device_is_available(child))
> > > > + continue;
> > > > +
> > > > + compatible = of_get_property(child, "compatible", &cplen);
> > > > + if (!compatible || strlen(compatible) > cplen)
> > > > + continue;
> > > > +
> > > > + if (strstr(compatible, "-usart")) {
> > > > + opmode = FLEX_MR_OPMODE_USART;
> > > > + break;
> > > > + }
> > > > +
> > > > + if (strstr(compatible, "-spi")) {
> > > > + opmode = FLEX_MR_OPMODE_SPI;
> > > > + break;
> > > > + }
> > > > +
> > > > + if (strstr(compatible, "-i2c")) {
> > > > + opmode = FLEX_MR_OPMODE_TWI;
> > > > + break;
> > > > + }
> > > > + }
> > >
> > > From what I understand Flexcom is a wrapper which can sit above any
> > > number of SPI, I2C and/or UART devices. Devices which you don't
> > > really have any control over (source code wise). So wouldn't it be
> > > better to match on the details you do have control over i.e. the node
> > > name, rather than the compatible string?
> > >
> > > I would personally match on of_find_node_by_name() to future-proof
> > > your implementation.
> >
> > Actually, I think using compatible strings is more future-proof than
> > using the node names, because nothing in the DT bindings doc enforce the
> > node name, and usually what we use to attach a node to a specific
> > driver is the compatible string (this one is specified in the bindings
> > doc).
>
> I know what you're saying, but what if someone uses the Flexcom driver
> to wrap a different type of SPI driver where (for instance) the
> compatible string used is "<name>-<newtype>". Then we'd have to keep
> adding more lines here to accommodate.
>
> Whereas if we used the child node name which only pertains to _this_
> driver, we would then have full control and know that (unless it
> Flexcom is used for a completely different type of serial controller)
> we wouldn't have to keep expanding the code to accommodate.
You're right about the complexity implied by the compat string
maintenance, but I still think using node names to detect the mode is
a bad idea.
Let's take another example making both solution unsuitable: what if
the flexcom-v2 exposes 2 devices of the same type, they will both have
the same name and the same compatible string, and we'll have no way to
detect the appropriate mode. That's why I think none of our suggestion
is future-proof.
>
> > Regarding the implementation itself, I would match the child node with
> > an of_device_id table rather than trying to find a specific substring
> > in the compatible string, but I think that's only a matter of taste.
>
> You mean duplicate each of the supported device's compatible strings
> in this driver, then fetch the attributed of_match_device()->data
> value?
>
Yes, and that's definitely not a good idea, but I think Cyrille has
found a better approach (I'll let him explain).
Best Regards,
Boris
--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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