Re: [alsa-devel] Why my linux OS has only 8 sound cards ? How can I modify it ?
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At Wed, 9 Nov 2011 10:24:41 +0800, 沈发旺 wrote:
Hi,Takashi Iwai : * I used your patch ,but it also display this when I used the command "ls /dev/dsp*".* */dev/dsp /dev/dsp2 /dev/dsp4 /dev/dsp6 /dev/dsp1 /dev/dsp3 /dev/dsp5 /dev/dsp7* *It also display this when board up:* *input: C-Media USB Headphone Set as /devices/platform/fsl-ehci.1/usb2/2-1/2-1.5/2-1.5:1.3/input/input7 generic-usb 0003:0D8C:000C.0007: input: USB HID v1.00 Device [C-Media USB Headphone Set ] on usb-fsl-ehci.1-1.5/input3 usb 2-1.6: new full speed USB device using fsl-ehci and address 8 unable to register OSS PCM device 8:0 unable to register OSS mixer device 8:0 input: C-Media USB Headphone Set as /devices/platform/fsl-ehci.1/usb2/2-1/2-1.6/2-1.6:1.3/input/input8 generic-usb 0003:0D8C:000C.0008: input: USB HID v1.00 Device [C-Media USB Headphone Set ] on usb-fsl-ehci.1-1.6/input3 usb 2-1.7: new full speed USB device using fsl-ehci and address 9 unable to register OSS PCM device 9:0 unable to register OSS mixer device 9:0 input: C-Media USB Headphone Set as /devices/platform/fsl-ehci.1/usb2/2-1/2-1.7/2-1.7:1.3/input/input9 generic-usb 0003:0D8C:000C.0009: input: USB HID v1.00 Device [C-Media USB Headphone Set ] on usb-fsl-ehci.1-1.7/input3 **when the sound cards exceed 8 ,I found it return err from sound/sound_core.c:__sound_insert_unit( ) . I read this code and found modify the function of "register_sound_special_device " -> max_unit = 128 + chain; when I change to :** max_unit = 256 + chain, my board will display 10 sound cards :*
So it's a limitation in sound_core.c. (BTW, 256+chain is wrong. It should be simply 256.)
I vaguely remember why we left the limit 8 in ALSA side. One reason was that sound_core itself doesn't support more than 8, and we weren't sure whether changing it would regress or not. For example, don't apps expect only a single digit after /dev/dsp?
OTOH, having 11 sound devices with OSS must be a rare case and I'm sure a legacy system using OSS won't have such a configuration. And fixing the code is basically a right thing.
That being said, I'm fine to change that part for the upstream, if no one objects.
thanks,
Takashi
/dev/dsp /dev/dsp2 /dev/dsp4 /dev/dsp6 /dev/dsp8 /dev/dsp1 /dev/dsp3 /dev/dsp5 /dev/dsp7 /dev/dsp9 *Thank you vary mach !* 2011/11/9 Takashi Iwai tiwai@suse.de
At Tue, 08 Nov 2011 18:37:53 +0100, Clemens Ladisch wrote:
Takashi Iwai wrote:
Linus Torvalds wrote:
Takashi, any idea? Do we have some 8-sound-card limit somewhere?
I do see that we have that odd
if (card && card->number >= 8) return 0; /* ignore silently */in sound/core/sound_oss.c: snd_register_oss_device(), but it has no comments. The thing goes back to 2005 with the commit log entry of "[ALSA] dynamic minors (6/6): increase maximum number of sound
cards",
but the value '8'isn't explained.
ALSA itself can support 32 cards when CONFIG_SND_DYNAMIC_MINORS is set ... The above code is, however, about OSS-emulation. And I guess it's just a left-over of the old static limitation.
Yes; I didn't change the limit in the OSS emulation because the minor number layout doesn't have space for all 32 cards, and extending the limit to 16 did not seem worth the effort for a 'legacy' interface.
Actually OSS could support up to 16 cards (in theory).
Below is an untested fix patch. Does it work?
Not without increasing SNDRV_OSS_MINORS, too:
Ah, good catch. Below is the revised patch.
Takashi
From: Takashi Iwai tiwai@suse.de Subject: [PATCH] ALSA: Fix the card number limit of OSS-emulation
There are left-over codes from the ancient days with the static device number limitation of 8. Actaully OSS can support up to 16 cards.
Signed-off-by: Takashi Iwai tiwai@suse.de
v2: fix SNDRV_OSS_MINORS, too
sound/core/sound_oss.c | 6 +++--- 1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/sound/core/sound_oss.c b/sound/core/sound_oss.c index c700920..e952833 100644 --- a/sound/core/sound_oss.c +++ b/sound/core/sound_oss.c @@ -35,7 +35,7 @@ #include <linux/sound.h> #include <linux/mutex.h>
-#define SNDRV_OSS_MINORS 128 +#define SNDRV_OSS_MINORS 256
static struct snd_minor *snd_oss_minors[SNDRV_OSS_MINORS]; static DEFINE_MUTEX(sound_oss_mutex); @@ -111,7 +111,7 @@ int snd_register_oss_device(int type, struct snd_card *card, int dev, int register1 = -1, register2 = -1; struct device *carddev = snd_card_get_device_link(card);
if (card && card->number >= 8)
if (card && card->number >= SNDRV_MINOR_OSS_DEVICES) return 0; /* ignore silently */ if (minor < 0) return minor;@@ -170,7 +170,7 @@ int snd_unregister_oss_device(int type, struct snd_card *card, int dev) int track2 = -1; struct snd_minor *mptr;
if (card && card->number >= 8)
if (card && card->number >= SNDRV_MINOR_OSS_DEVICES) return 0; if (minor < 0) return minor;-- 1.7.7
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-
Takashi Iwai