linux-kernel - Re: [PATCH v1 1/2] tty/vt: Use KVAL instead of use bit operation

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Message-ID: <8b2200ea-425d-477d-8463-d49eb1c7a66a@kernel.org>
Date: Wed, 19 Feb 2025 10:33:38 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Alexey Gladkov <legion@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 LKML <linux-kernel@...r.kernel.org>, linux-serial@...r.kernel.org
Subject: Re: [PATCH v1 1/2] tty/vt: Use KVAL instead of use bit operation

On 19. 02. 25, 10:23, Alexey Gladkov wrote:
> On Wed, Feb 19, 2025 at 07:24:52AM +0100, Jiri Slaby wrote:
>> On 18. 02. 25, 13:29, Alexey Gladkov wrote:
>>> The K_HANDLERS always gets KVAL as an argument. It is better to use the
>>> KVAL macro itself instead of bit operation.
>>>
>>> Signed-off-by: Alexey Gladkov <legion@...nel.org>
>>> ---
>>>    drivers/tty/vt/keyboard.c | 4 ++--
>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
>>> index 804355da46f5..7df041ac4d5c 100644
>>> --- a/drivers/tty/vt/keyboard.c
>>> +++ b/drivers/tty/vt/keyboard.c
>>> @@ -885,7 +885,7 @@ static void k_shift(struct vc_data *vc, unsigned char value, char up_flag)
>>>    		if (kbd->kbdmode == VC_UNICODE)
>>>    			to_utf8(vc, npadch_value);
>>>    		else
>>> -			put_queue(vc, npadch_value & 0xff);
>>> +			put_queue(vc, KVAL(npadch_value));
>>
>> While the mask is the same, this is not a kval, right?
> 
> I'm pretty sure it's KVAL, but to be honest I don't understand why it is
> not done for to_utf8() as well. All values passed to to_utf8() must be
> kval.

Not at all, it handles multibyte chars.

> We call to_utf8() in k_unicode, fn_enter (through k_spec), handle_diacr
> (through k_deadunicode or k_unicode). All K_HANDLERS take KVAL as value.

Yes, but pass unicode multibyte to to_utf8().

> If I understand this code correctly, it is more correct to write it like
> this:
> 
> --- a/drivers/tty/vt/keyboard.c
> +++ b/drivers/tty/vt/keyboard.c
> @@ -882,10 +882,11 @@ static void k_shift(struct vc_data *vc, unsigned char value, char up_flag)
> 
>          /* kludge */
>          if (up_flag && shift_state != old_state && npadch_active) {
> +               u32 kval = KVAL(npadch_value);
>                  if (kbd->kbdmode == VC_UNICODE)
> -                       to_utf8(vc, npadch_value);
> +                       to_utf8(vc, kval);

Definitely not, as you want to pass that multibyte char in.

-- 
js
suse labs