Re: [alsa-devel] [PATCH] ALSA: usb-audio: Add support for Presonus Studio 1810c

On Wed, 25 Dec 2019 03:34:24 +0100, mickflemm@gmail.com wrote:

This patch adds support for Presonus Studio 1810c, a usb interface that's UAC2 compliant with a few quirks and a few extra hw-specific controls. I've tested all 3 altsettings and the added switch controls and they work as expected.

More infos on the card: https://www.presonus.com/products/Studio-1810c

Note that this work is based on packet inspection with usbmon. I just wanted to get this card to work for using it on our open-source radio station: https://github.com/UoC-Radio

Signed-off-by: Nick Kossifidis mickflemm@gmail.com

Thanks for the patch.

In addition to the issues kbuild bot suggested, below are my quick review comments:

diff --git a/sound/usb/format.c b/sound/usb/format.c index d79db7130..edf3f2a55 100644 --- a/sound/usb/format.c +++ b/sound/usb/format.c @@ -262,6 +262,23 @@ static int parse_uac2_sample_rate_range(struct snd_usb_audio *chip, }

for (rate = min; rate <= max; rate += res) {

• 	/*
  

• 	 * Presonus Studio 1810c anounces invalid
  

• 	 * sampling rates for its streams.
  

• 	 */
  

• 	if (chip->usb_id == USB_ID(0x0194f, 0x010c) &&
  

• 	((rate > 48000 && fp->altsetting == 1) ||
  

• 	 ((rate < 88200 || rate > 96000)
  

• 	  && fp->altsetting == 2) ||
  

• 	 ((rate < 176400 || rate > 192000)
  

• 	  && fp->altsetting == 3))) {
  

• 		if (res)
  

• 			continue;
  

• 		else
  

• 			break;
  

• 	}
  

It's hard to imagine what result this would lead to, because the conditions are so complex. Maybe better to prepare a fixed table instead? Or, can we simply take a fixed quirk?

diff --git a/sound/usb/mixer_s1810c.c b/sound/usb/mixer_s1810c.c new file mode 100644 index 000000000..ff86e4aab --- /dev/null +++ b/sound/usb/mixer_s1810c.c @@ -0,0 +1,565 @@ +// SPDX-License-Identifier: GPL-2.0 +/*

• • Presonus Studio 1810c driver for ALSA
• • Copyright (C) 2019 Nick Kossifidis mickflemm@gmail.com
• • Based on reverse engineering of the communication protocol
• • between the windows driver / Univeral Control (UC) program
• • and the device, through usbmon.
• • For now this bypasses the mixer, with all channels split,
• • so that the software can mix with greater flexibility.
• • It also adds controls for the 4 buttons on the front of
• • the device.
• */

Usually place a blank line here.

+#include <linux/usb.h> +#include <linux/usb/audio-v2.h> +#include <sound/control.h> +#include <linux/slab.h>

The common practice is to group linux/*.h first, followed by sound/*.h. And <sound/core.h> is almost always needed before other sound/*.h.

+struct s1810c_ctl_packet {

• uint32_t a;
• uint32_t b;
• uint32_t fixed1;
• uint32_t fixed2;
• uint32_t c;
• uint32_t d;
• uint32_t e;

Use u32, u16 or such types instead of uint*_t. It's the standard type for kernel codes. Also applied in other places in the patch, too.

+static int +snd_sc1810c_get_status_field(struct usb_device *dev,

• 	     uint32_t *field, int field_idx, uint16_t *seqnum)
  

+{

• struct s1810c_state_packet pkt_out = { 0 };
• struct s1810c_state_packet pkt_in = { 0 };
• int ret = 0;
• pkt_out.fields[SC1810C_STATE_F1_IDX] = SC1810C_SET_STATE_F1;
• pkt_out.fields[SC1810C_STATE_F2_IDX] = SC1810C_SET_STATE_F2;
• ret = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0),

• 	      SC1810C_SET_STATE_REQ,
  

• 	      SC1810C_SET_STATE_REQTYPE,
  

• 	      (*seqnum), 0, &pkt_out, sizeof(pkt_out));
  

Avoid unnecessary parentheses around *seqnum. Ditto for other possible places.

+static int +snd_s1810c_switch_set(struct snd_kcontrol *kctl,

•       struct snd_ctl_elem_value *ctl_elem)
  

+{

• struct usb_mixer_elem_list *list = snd_kcontrol_chip(kctl);
• struct usb_mixer_interface *mixer = list->mixer;
• uint32_t curval = 0;
• uint32_t newval = (uint32_t) ctl_elem->value.integer.value[0];
• int ret = 0;
• ret = snd_s1810c_get_switch_state(mixer, kctl, &curval);
• if (ret < 0)

• return 0;
  

• if (curval == newval)

• return 0;
  

• kctl->private_value &= ~(0x1 << 16);
• kctl->private_value |= (unsigned int)(newval & 0x1) << 16;
• ret = snd_s1810c_set_switch_state(mixer, kctl);

Hm, this can be racy. The control get/put isn't protected, so you might get the inconsistency here when multiple kctls are accessed concurrently.

+static int +snd_s1810c_line_sw_info(struct snd_kcontrol *kctl,

• 	struct snd_ctl_elem_info *uinfo)
  

+{

• static const char *const texts[2] = { "Preamp on (Mic/Inst)",

• "Preamp off (Line in)"
  

• };

Better to put "Preamp on..." item in the next line.

+static struct snd_kcontrol_new snd_s1810c_line_sw = {

This (and other following definitions) can be const?

• .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
• .name = "Line 1/2 source type",

The control name should consist of words starting with a capital letter, so it should be "Line 1/2 Source Type". Also, usually a control name needs a standard suffix. Though, this has a special return enum type, so it can be OK as is.

However...

• .info = snd_s1810c_line_sw_info,
• .get = snd_s1810c_switch_get,
• .put = snd_s1810c_switch_set,

... this shows that the combination is invalid. The enum type doesn't get/put the values in integer fields. It's incompatible.

• .private_value = (SC1810C_STATE_LINE_SW | SC1810C_CTL_LINE_SW << 8)

+};

+static struct snd_kcontrol_new snd_s1810c_mute_sw = {

• .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
• .name = "Mute Main Out",

... and this one, for example, should deserve for "Switch" suffix, as it's a standard boolean switch (which use integer fields unlike enum).

+/* Entry point, called from mixer_quirks.c */ +int snd_sc1810_init_mixer(struct usb_mixer_interface *mixer) +{

• struct s1810_mixer_state *private = NULL;
• struct snd_usb_audio *chip = mixer->chip;
• struct usb_device *dev = chip->dev;
• int ret = 0;
• /* Run this only once */
• if (!list_empty(&chip->mixer_list))

• return 0;
  

• dev_info(&dev->dev,

•  "Presonus Studio 1810c, device_setup: %u\n", chip->setup);
  

• if (chip->setup == 1)

• dev_info(&dev->dev, "(8out/18in @ 48KHz)\n");
  

• else if (chip->setup == 2)

• dev_info(&dev->dev, "(6out/8in @ 192KHz)\n");
  

• else

• dev_info(&dev->dev, "(8out/14in @ 96KHz)\n");
  

• ret = snd_s1810c_init_mixer_maps(chip);
• if (ret < 0)

• return ret;
  

• private = vzalloc(sizeof(struct s1810_mixer_state));

I don't think vmalloc is needed here, as the object is so small. Use kzalloc() and kfree() instead (unless I overlook something).

• if (!private) {

• dev_err(&dev->dev, "could not allocate mixer state\n");
  

The error message is usually superfluous, as kernel spews the warning in anyway at each allocation error.

thanks,

Takashi