On Wed, Apr 01, 2015 at 12:19:25PM -0600, Jason Gunthorpe wrote:
> On Wed, Apr 01, 2015 at 03:28:52PM +0300, Jarkko Sakkinen wrote:
> > Added PPI interface to the character device. PPI interface is also kept
> > in the pdev for backwards compatibility.
>
> Could you look at just completely moving the PPI interface to the char
> dev and then adding a symlink from the pdev? That would be really
> ideal.
>
> symlinks have the advantage that they actually fully fix the lifetime
> issues.
>
> This seems doable, if we replace the ppi_attrs group with a bunch of
> calls to sysfs_create_link it should work ?
If we follow the pattern in [1] by the book, how would you use
sysfs_create_link()? To be more specific, how would you get the driver
core to create the symlinks for you?
If we decide not to follow [1] by the book, then this might be doable
(thinking off my head, that's the reason why I use *might be* instead
of *is*). Wouldn't we get non-racy behavior if sysfs_create_link()'s
are executed after device_initialize() and before device_add()?
> > +static struct tpm_chip *ppi_dev_to_chip(struct device *dev)
> > +{
> > + struct tpm_chip *chip = dev_get_drvdata(dev);
> > +
> > + if (chip == NULL)
> > + chip = to_tpm_chip(chip);
> > +
> > + return chip;
> > +}
>
> If symlinks don't work out, we should probably just set the drvdata on
> the tpm_chip itself to avoid this.
I'll experiment with this. Thanks for the comment.
> > + if (!(chip->flags & TPM_CHIP_FLAG_PPI))
> > + return -EINVAL;
>
> Hum, I don't think the PPI files should be created if there is no PPI
> support..
Again, following [1] by the book. And again, I think we could just as
well do our sysfs stuff in-between device_initialize() and device_add()
and get the non-racy behavior.
> > +void __init tpm_ppi_init(struct class *tpm_class)
> > +{
> > + tpm_class->dev_groups = tpm_groups;
> > }
>
> So this shouldn't be unconditional.
>
> Also, ultimately PPI can't just claim the dev_groups, other parts of
> the driver will need to add groups too.
>
> I think it makes more sense to do
>
> struct attribute_group *tpm_ppi_get_sysfs(struct tpm_chip *chip)
> {
> }
>
> And take care of building the list in the caller.
>
> And tpm_ppi_get_sysfs should be called after the driver is readied but
> before adding the device.
I don't think this would matter. Things could be refactored when more
sysfs attributes are needed.
> Jason
/Jarkko
[1] http://kroah.com/log/blog/2013/06/26/how-to-create-a-sysfs-file-correctly/
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