linux-kernel - Re: [PATCH] auxdisplay: ht16k33: use le16_to

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Message-ID: <20170329101359.3d928ff8@erd979>
Date:   Wed, 29 Mar 2017 10:13:59 +0200
From:   Robin van der Gracht <robin@...tonic.nl>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>,
        Arnd Bergmann <arnd@...db.de>, Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] auxdisplay: ht16k33: use le16_to_cpup() to fetch LE16
 data

On Wed, 29 Mar 2017 00:42:08 -0700
Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:

> The data read from the device is 3 little-endian words, so let's annotate
> them as such and use le16_to_cpu() to convert them to host endianness - it
> might turn out to be a bit more performant, and it expresses the conversion
> more clearly.

Agreed

> 
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> ---
>  drivers/auxdisplay/ht16k33.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/auxdisplay/ht16k33.c b/drivers/auxdisplay/ht16k33.c
> index f66b45b235b0..61af52a7afd5 100644
> --- a/drivers/auxdisplay/ht16k33.c
> +++ b/drivers/auxdisplay/ht16k33.c
> @@ -254,18 +254,19 @@ static bool ht16k33_keypad_scan(struct ht16k33_keypad *keypad)
>  {
>  	const unsigned short *keycodes = keypad->dev->keycode;
>  	u16 new_state[HT16K33_MATRIX_KEYPAD_MAX_COLS];
> -	u8 data[HT16K33_MATRIX_KEYPAD_MAX_COLS * 2];
> +	__le16 data[HT16K33_MATRIX_KEYPAD_MAX_COLS];
>  	unsigned long bits_changed;
>  	int row, col, code;
>  	bool pressed = false;
>  
> -	if (i2c_smbus_read_i2c_block_data(keypad->client, 0x40, 6, data) != 6) {
> +	if (i2c_smbus_read_i2c_block_data(keypad->client, 0x40,
> +					  sizeof(data), (u8 *)data) != 6) {

Why use sizeof(data) for length but check against the hardcoded 6?

>  		dev_err(&keypad->client->dev, "Failed to read key data\n");
>  		return false;
>  	}
>  
>  	for (col = 0; col < keypad->cols; col++) {
> -		new_state[col] = (data[col * 2 + 1] << 8) | data[col * 2];
> +		new_state[col] = le16_to_cpu(data[col]);

nice!

>  		if (new_state[col])
>  			pressed = true;
>  		bits_changed = keypad->last_key_state[col] ^ new_state[col];

Robin