linux-kernel - Re: [PATCH v4 1/5] ALSA: usb-audio: add two-way convert between name and bit for QUIRK_FLAG

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Message-ID: <87tt0y8vxx.wl-tiwai@suse.de>
Date: Fri, 19 Sep 2025 14:32:10 +0200
From: Takashi Iwai <tiwai@...e.de>
To: cryolitia@...ontech.com
Cc: Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Daniel Gomez <da.gomez@...nel.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	linux-sound@...r.kernel.org,
	linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org,
	Mingcong Bai <jeffbai@...c.io>,
	Kexy Biscuit <kexybiscuit@...c.io>,
	Nie Cheng <niecheng1@...ontech.com>,
	Zhan Jun <zhanjun@...ontech.com>,
	Feng Yuan <fengyuan@...ontech.com>,
	qaqland <anguoli@...ontech.com>,
	kernel@...ontech.com,
	linux-modules@...r.kernel.org
Subject: Re: [PATCH v4 1/5] ALSA: usb-audio: add two-way convert between name and bit for QUIRK_FLAG_*

On Thu, 18 Sep 2025 11:24:30 +0200,
Cryolitia PukNgae via B4 Relay wrote:
> --- a/sound/usb/quirks.c
> +++ b/sound/usb/quirks.c
> @@ -2446,6 +2446,62 @@ static const struct usb_audio_quirk_flags_table quirk_flags_table[] = {
>  	{} /* terminator */
>  };
>  
> +static const char *const snd_usb_audio_quirk_flag_names[] = {
> +	"get_sample_rate",
> +	"share_media_device",

I think it's worth to add a comment that this each entry corresponds
to QUIRK_FLAG_XXX.  Or another idea would be to define enums like:

enum {
	QUIRK_TYPE_GET_SAMPLE_RATE,
	QUIRK_TYPE_SHARE_MEDIA_DEVICE,
	....
};

then redefine QUIRK_FLAG_* like:

#define QUIRK_FLAG_GET_SAMPLE_RATE	BIT_U32(QUIRK_TYPE_GET_SAMPLE_RATE)
#define QUIRK_FLAG_SHARE_MEDIA_DEVICE	BIT_U32(QUIRK_TYPE_SHARE_MEDIA_DEVICE)
....
 
or

#define QUIRK_FLAG(x)	BIT_U32(QUIRK_TYPE_ ## x)

and use like QUIRK_FLAG(GET_SAMPLE_RATE).

With those changes, the above can be defined more safely like

static const char *const snd_usb_audio_quirk_flag_names[] = {
	[QUIRK_TYPE_GET_SAMPLE_RATE] = "get_sample_rate",
	....

or even more drastically by defining some macro for each entry like:

#define QUIRK_STRING_ENTRY(x) \
	[QUIRK_TYPE_ ## x] = __stringify(x)

and put like:

static const char *const snd_usb_audio_quirk_flag_names[] = {
	QUIRK_STRING_ENTRY(GET_SAMPLE_RATE),
	....
};

In this case, it'll become upper letters, so the parse would need to
deal with the case-insensitive comparison, though.

> +u32 snd_usb_quirk_flags_from_name(char *name)

Use const char *.

> +{
> +	u32 flag = 0;
> +	u32 i;

The iterator can be simple int.

> +	if (!name || !*name)
> +		return 0;
> +
> +	for (i = 0; snd_usb_audio_quirk_flag_names[i]; i++) {
> +		if (strcmp(name, snd_usb_audio_quirk_flag_names[i]) == 0) {
> +			flag = (1U << i);

Use BIT_U32(i)

> +			break;

We can return the value directly, so flag variable can be dropped.

>  void snd_usb_init_quirk_flags(struct snd_usb_audio *chip)
>  {
>  	const struct usb_audio_quirk_flags_table *p;
> @@ -2454,10 +2510,28 @@ void snd_usb_init_quirk_flags(struct snd_usb_audio *chip)
>  		if (chip->usb_id == p->id ||
>  		    (!USB_ID_PRODUCT(p->id) &&
>  		     USB_ID_VENDOR(chip->usb_id) == USB_ID_VENDOR(p->id))) {
> -			usb_audio_dbg(chip,
> -				      "Set quirk_flags 0x%x for device %04x:%04x\n",
> -				      p->flags, USB_ID_VENDOR(chip->usb_id),
> -				      USB_ID_PRODUCT(chip->usb_id));
> +			unsigned long flags = p->flags;
> +			unsigned long bit;
> +
> +			for_each_set_bit(bit, &flags,
> +					 BYTES_TO_BITS(sizeof(p->flags))) {
> +				const char *name =
> +					snd_usb_audio_quirk_flag_names[bit];
> +
> +				if (name)
> +					usb_audio_dbg(chip,
> +						      "Set quirk flag %s for device %04x:%04x\n",
> +						      name,
> +						      USB_ID_VENDOR(chip->usb_id),
> +						      USB_ID_PRODUCT(chip->usb_id));
> +				else
> +					usb_audio_warn(chip,
> +						       "Set unknown quirk flag 0x%lx for device %04x:%04x\n",
> +						       bit,
> +						       USB_ID_VENDOR(chip->usb_id),
> +						       USB_ID_PRODUCT(chip->usb_id));
> +			}

This could be better factored out as a function.


thanks,

Takashi