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Date:   Tue, 12 Jan 2021 15:55:28 -0800
From:   Philip Chen <philipchen@...omium.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Douglas Anderson <dianders@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Guenter Roeck <groeck@...omium.org>,
        Lee Jones <lee.jones@...aro.org>, linux-input@...r.kernel.org
Subject: Re: [PATCH v4 2/2] Input: cros-ec-keyb - Expose function row physical
 map to userspace

On Mon, Jan 11, 2021 at 6:24 PM Stephen Boyd <swboyd@...omium.org> 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`?
>
> >
> > Signed-off-by: Philip Chen <philipchen@...omium.org>
> > ---
> >
> > Changes in v4:
> > - replace sysfs_create_group() with devm_device_add_group()
> > - remove an unused member in struct cros_ec_keyb
> >
> > Changes in v3:
> > - parse `function-row-physmap` from DT earlier, when we probe
> >   cros_ec_keyb, and then store the extracted info in struct cros_ec_keyb.
> >
> > Changes in v2:
> > - create function-row-physmap file in sysfs by parsing
> >   `function-row-physmap` property from DT
> > - assume the device already has a correct keymap to reflect the custom
> >   top-row keys (if they exist)
> >
> >  drivers/input/keyboard/cros_ec_keyb.c | 78 +++++++++++++++++++++++++++
> >  1 file changed, 78 insertions(+)
> >
> > diff --git a/drivers/input/keyboard/cros_ec_keyb.c b/drivers/input/keyboard/cros_ec_keyb.c
> > index b379ed7628781..75d1cb29734ce 100644
> > --- a/drivers/input/keyboard/cros_ec_keyb.c
> > +++ b/drivers/input/keyboard/cros_ec_keyb.c
> > @@ -27,6 +27,8 @@
> >
> >  #include <asm/unaligned.h>
> >
> > +#define MAX_NUM_TOP_ROW_KEYS   15
> > +
>
> Ah, the binding could say max is 15 then.
Yes, I'll add the documentation to PATCH 1/2.
>
> >  /**
> >   * 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?
>
> >  };
> >
> >  /**
> > @@ -527,6 +535,8 @@ static int cros_ec_keyb_register_matrix(struct cros_ec_keyb *ckdev)
> >         struct input_dev *idev;
> >         const char *phys;
> >         int err;
> > +       u32 top_row_key_pos[MAX_NUM_TOP_ROW_KEYS] = {0};
> > +       u8 i;
> >
> >         err = matrix_keypad_parse_properties(dev, &ckdev->rows, &ckdev->cols);
> >         if (err)
> > @@ -578,6 +588,22 @@ static int cros_ec_keyb_register_matrix(struct cros_ec_keyb *ckdev)
> >         ckdev->idev = idev;
> >         cros_ec_keyb_compute_valid_keys(ckdev);
> >
> > +       if (of_property_read_variable_u32_array(dev->of_node,
> > +                                               "function-row-physmap",
> > +                                               top_row_key_pos,
> > +                                               0,
> > +                                               MAX_NUM_TOP_ROW_KEYS) > 0) {
> > +               for (i = 0; i < MAX_NUM_TOP_ROW_KEYS; i++) {
>
> Can we deindent this once with of_property_for_each_u32()?
Sure, will do.
>
> > +                       if (!top_row_key_pos[i])
> > +                               break;
> > +                       ckdev->function_row_physmap[i] = MATRIX_SCAN_CODE(
> > +                                               KEY_ROW(top_row_key_pos[i]),
> > +                                               KEY_COL(top_row_key_pos[i]),
>
> And then have a local variable for top_row_key_pos[i] so this is
> shorter.
Sure, will do.
>
> > +                                               ckdev->row_shift);
> > +               }
> > +               ckdev->num_function_row_keys = i;
> > +       }
> > +
> >         err = input_register_device(ckdev->idev);
> >         if (err) {
> >                 dev_err(dev, "cannot register input device\n");
> > @@ -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?
>
> > +       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.
Thanks!

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