linux-kernel - Re: [PATCH v4 2/2] Input: add Apple SPI keyboard and trackpad driver.

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Date:   Mon, 8 Apr 2019 20:23:31 -0700
From:   "Life is hard, and then you die" <ronald@...ovation.ch>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Henrik Rydberg <rydberg@...math.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Lukas Wunner <lukas@...ner.de>,
        Federico Lorenzi <federico@...velground.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] Input: add Apple SPI keyboard and trackpad driver.


On Mon, Apr 08, 2019 at 03:33:43PM +0300, Andy Shevchenko wrote:
> On Sat, Apr 06, 2019 at 10:03:58PM -0700, Ronald Tschalär wrote:
> > The keyboard and trackpad on recent MacBook's (since 8,1) and
> > MacBookPro's (13,* and 14,*) are attached to an SPI controller instead
> > of USB, as previously. The higher level protocol is not publicly
> > documented and hence has been reverse engineered. As a consequence there
> > are still a number of unknown fields and commands. However, the known
> > parts have been working well and received extensive testing and use.
> > 
> > In order for this driver to work, the proper SPI drivers need to be
> > loaded too; for MB8,1 these are spi_pxa2xx_platform and spi_pxa2xx_pci;
> > for all others they are spi_pxa2xx_platform and intel_lpss_pci. For this
> > reason enabling this driver in the config implies enabling the above
> > drivers.
> 
> Thank you for an update, my comments below.

Thank you again for your review.

[snip]
> > +	} else {
> > +		struct dentry *ret;
> > +
> > +		ret = debugfs_create_bool("enable_tp_dim", 0600,
> > +					  applespi->debugfs_root,
> > +					  &applespi->debug_tp_dim);
> > +		if (IS_ERR(ret))
> > +			dev_warn(&(applespi)->spi->dev,
> > +				 "Error creating debugfs entry enable_tp_dim (%ld)\n",
> > +				 PTR_ERR(ret));
> 
> Can ret be NULL?

No, it actually can't (I manually traced all code paths to be sure):
the documentation for these helper functions is wrong in this respect.
However, I note that a lot of existing kernel code also has this wrong
(i.e. it's checking for NULL). Digging a bit further and looking at
the history, it appears this was changed just recently (commit
ff9fb72b "debugfs: return error values, not NULL"), which would
explain the existing code and documentation. I'll submit a patch to
update the docs.

> dev_dbg() looks more appropriate.

Hmm, ok, I guess I find this a bit odd, though: true, this only
affects code used for debugging, but it's nevertheless an error that
shouldn't normally occur.


  Cheers,

  Ronald