Quoting Philip Chen (2021-01-12 15:55:28)
> On Mon, Jan 11, 2021 at 6:24 PM Stephen Boyd <swboyd@xxxxxxxxxxxx> wrote:
> >
> > Quoting Philip Chen (2021-01-07 15:42:09)
> > > The top-row keys in a keyboard usually have dual functionalities.
> > > E.g. A function key "F1" is also an action key "Browser back".
> > >
> > > Therefore, when an application receives an action key code from
> > > a top-row key press, the application needs to know how to correlate
> > > the action key code with the function key code and do the conversion
> > > whenever necessary.
> > >
> > > Since the userpace already knows the key scanlines (row/column)
> > > associated with a received key code. Essentially, the userspace only
> > > needs a mapping between the key row/column and the matching physical
> > > location in the top row.
> > >
> > > This patch enhances the cros-ec-keyb driver to create such a mapping
> > > and expose it to userspace in the form of a function-row-physmap
> > > attribute. The attribute would be a space separated ordered list of
> > > row/column codes, for the keys in the function row, in a left-to-right
> > > order.
> > >
> > > The attribute will only be present when the device has a custom design
> > > for the top-row keys.
> >
> > Is it documented in Documentation/ABI/?
> Not yet.
> Is it proper to add the documentation to `testing/sysfs-driver-input-keyboard`?
Somewhere in testing is fine. I'm not sure if it is a generic proprty
for all keyboards though? What's the path in sysfs?
> >
> > >
> > > /**
> > > * struct cros_ec_keyb - Structure representing EC keyboard device
> > > *
> > > @@ -42,6 +44,9 @@
> > > * @idev: The input device for the matrix keys.
> > > * @bs_idev: The input device for non-matrix buttons and switches (or NULL).
> > > * @notifier: interrupt event notifier for transport devices
> > > + * @function_row_physmap: An array of the encoded rows/columns for the top
> > > + * row function keys, in an order from left to right
> > > + * @num_function_row_keys: The number of top row keys in a custom keyboard
> > > */
> > > struct cros_ec_keyb {
> > > unsigned int rows;
> > > @@ -58,6 +63,9 @@ struct cros_ec_keyb {
> > > struct input_dev *idev;
> > > struct input_dev *bs_idev;
> > > struct notifier_block notifier;
> > > +
> > > + u16 function_row_physmap[MAX_NUM_TOP_ROW_KEYS];
> > > + u8 num_function_row_keys;
> >
> > Why not size_t?
> I usually try to use the minimal required bytes for variables, even
> for local ones.
> In this case, we only need one byte for num_function_row_keys.
> Are there any reasons why size_t is better?
I suppose to indicate that it's an array size. It's not a super strong
argument but the usage of u8 looks like we're trying to save space in a
single structure instance (or maybe a couple if there are a few
keyboards), when for all I know it actually generates worse code because
it has to do some masking operation on the load from memory when it
could just load the value directly into a register.
> >
> > > };
> > >
> > > /**
> > > @@ -587,6 +613,52 @@ static int cros_ec_keyb_register_matrix(struct cros_ec_keyb *ckdev)
> > > return 0;
> > > }
> > >
> > > +static ssize_t function_row_physmap_show(struct device *dev,
> > > + struct device_attribute *attr,
> > > + char *buf)
> > > +{
> > > + ssize_t size = 0;
> > > + u8 i;
> >
> > int i? Why u8? Surely the size of a local variable isn't important.
> The same reason as "u8 num_function_row_keys".
> Is int better in this case?
Yeah int is better because it's a local variable and nobody cares about
those extra few bytes.
> >
> > > + struct cros_ec_keyb *ckdev = dev_get_drvdata(dev);
> > > +
> > > + if (!ckdev->num_function_row_keys)
> > > + return 0;
> > > +
> > > + for (i = 0; i < ckdev->num_function_row_keys; i++)
> > > + size += scnprintf(buf + size, PAGE_SIZE - size, "%02X ",
> > > + ckdev->function_row_physmap[i]);
> > > + size += scnprintf(buf + size, PAGE_SIZE - size, "\n");
> > > +
> > > + return size;
> >
> > I'd rather see
> >
> > ssize_t size = 0;
> > int i;
> > struct cros_ec_keyb *ckdev = dev_get_drvdata(dev);
> > u16 *physmap = ckdev->function_row_physmap;
> >
> > for (i = 0; i < ckdev->num_function_row_keys; i++)
> > size += scnprintf(buf + size, PAGE_SIZE - size,
> > "%s%02X", size ? " " : "", physmap[i]);
> >
> > if (size)
> > size += scnprintf(buf + size, PAGE_SIZE - size, "\n");
> >
> > return size;
> >
> > And I wonder if hex_dump_to_buffer() works for this?
> It seems to work? I'll give it a try.
> If hex_dump_to_buffer() doesn't work, I'll fall back to the
> implementation you suggested above.
Ok sounds good.
