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 [off-list ref] wrote:

Quoting Philip Chen (2021-01-07 15:42:09)

quoted

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`?

quoted

Signed-off-by: Philip Chen <redacted>
---

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.

quoted

 /**
  * 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?

quoted

 };

 /**

@@ -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.

quoted

+                       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.

quoted

+                                               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?

quoted

+       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!