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Groups > linux.kernel > #1641363 > unrolled thread
| Started by | Geert Uytterhoeven <geert@linux-m68k.org> |
|---|---|
| First post | 2017-05-15 10:20 +0200 |
| Last post | 2017-05-15 16:50 +0200 |
| Articles | 5 — 2 participants |
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[PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in snd_tscm_stream_get_rate() Geert Uytterhoeven <geert@linux-m68k.org> - 2017-05-15 10:20 +0200
[PATCH 2/2] ALSA: firewire-tascam: Use do { } while for loops executed at least once Geert Uytterhoeven <geert@linux-m68k.org> - 2017-05-15 10:20 +0200
Re: [PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in snd_tscm_stream_get_rate() Takashi Sakamoto <o-takashi@sakamocchi.jp> - 2017-05-15 16:10 +0200
Re: [PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in snd_tscm_stream_get_rate() Geert Uytterhoeven <geert@linux-m68k.org> - 2017-05-15 16:30 +0200
Re: [PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in snd_tscm_stream_get_rate() Takashi Sakamoto <o-takashi@sakamocchi.jp> - 2017-05-15 16:50 +0200
| From | Geert Uytterhoeven <geert@linux-m68k.org> |
|---|---|
| Date | 2017-05-15 10:20 +0200 |
| Subject | [PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in snd_tscm_stream_get_rate() |
| Message-ID | <tHjou-5y7-13@gated-at.bofh.it> |
Obviously the intention was to put a limit on the maximum number of
operations. However, for this to work, the check should be
"&& trials++ < 5", not "|| trials++ < 5".
Fixes: 35efa5c489de63a9 ("ALSA: firewire-tascam: add streaming functionality")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
Compile-tested only.
Triggered by a false-positive warning from gcc-4.1.2:
warning: ‘err’ may be used uninitialized in this function
---
sound/firewire/tascam/tascam-stream.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/sound/firewire/tascam/tascam-stream.c b/sound/firewire/tascam/tascam-stream.c
index f1657a4e0621ef49..e433b92ac6904db5 100644
--- a/sound/firewire/tascam/tascam-stream.c
+++ b/sound/firewire/tascam/tascam-stream.c
@@ -84,7 +84,7 @@ int snd_tscm_stream_get_rate(struct snd_tscm *tscm, unsigned int *rate)
unsigned int trials = 0;
int err;
- while (data == 0x0 || trials++ < 5) {
+ while (data == 0x0 && trials++ < 5) {
err = get_clock(tscm, &data);
if (err < 0)
return err;
--
2.7.4
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| From | Geert Uytterhoeven <geert@linux-m68k.org> |
|---|---|
| Date | 2017-05-15 10:20 +0200 |
| Subject | [PATCH 2/2] ALSA: firewire-tascam: Use do { } while for loops executed at least once |
| Message-ID | <tHjov-5y7-53@gated-at.bofh.it> |
| In reply to | #1641363 |
If a loop is intended to be executed at least once, it is better to use
"do { ... } while (...)" instead of "while (...) { ... }".
The former is easier to understand for the casual reviewer, and doesn't
require preinitializing the canary variable.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
Compile-tested only.
---
sound/firewire/tascam/tascam-stream.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/sound/firewire/tascam/tascam-stream.c b/sound/firewire/tascam/tascam-stream.c
index e433b92ac6904db5..4ea6845aae87fdef 100644
--- a/sound/firewire/tascam/tascam-stream.c
+++ b/sound/firewire/tascam/tascam-stream.c
@@ -80,17 +80,17 @@ static int set_clock(struct snd_tscm *tscm, unsigned int rate,
int snd_tscm_stream_get_rate(struct snd_tscm *tscm, unsigned int *rate)
{
- u32 data = 0x0;
unsigned int trials = 0;
+ u32 data;
int err;
- while (data == 0x0 && trials++ < 5) {
+ do {
err = get_clock(tscm, &data);
if (err < 0)
return err;
data = (data & 0xff000000) >> 24;
- }
+ } while (data == 0x0 && ++trials < 5);
/* Check base rate. */
if ((data & 0x0f) == 0x01)
--
2.7.4
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| From | Takashi Sakamoto <o-takashi@sakamocchi.jp> |
|---|---|
| Date | 2017-05-15 16:10 +0200 |
| Subject | Re: [PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in snd_tscm_stream_get_rate() |
| Message-ID | <tHoRc-KQ-19@gated-at.bofh.it> |
| In reply to | #1641363 |
Hi,
On May 15 2017 17:19, Geert Uytterhoeven wrote:
> Obviously the intention was to put a limit on the maximum number of
> operations. However, for this to work, the check should be
> "&& trials++ < 5", not "|| trials++ < 5".
>
> Fixes: 35efa5c489de63a9 ("ALSA: firewire-tascam: add streaming functionality")
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
> Compile-tested only.
>
> Triggered by a false-positive warning from gcc-4.1.2:
>
> warning: ‘err’ may be used uninitialized in this function
> ---
> sound/firewire/tascam/tascam-stream.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sound/firewire/tascam/tascam-stream.c b/sound/firewire/tascam/tascam-stream.c
> index f1657a4e0621ef49..e433b92ac6904db5 100644
> --- a/sound/firewire/tascam/tascam-stream.c
> +++ b/sound/firewire/tascam/tascam-stream.c
> @@ -84,7 +84,7 @@ int snd_tscm_stream_get_rate(struct snd_tscm *tscm, unsigned int *rate)
> unsigned int trials = 0;
> int err;
>
> - while (data == 0x0 || trials++ < 5) {
> + while (data == 0x0 && trials++ < 5) {
> err = get_clock(tscm, &data);
> if (err < 0)
> return err;
Yep. It looks a bug.
...However, removal of the bug causes issue that the driver fails to
start a pair of capture/playback PCM substream when application requests
them mostly the same time, like jackd process.
I think I did apply the bug as a makeshift workaround, then forgot
itself when developing the driver... I'd like to have a bit time for
further investigation, then post my fix in this development period.
Please let me keep this patch pending.
Thanks
Takashi Sakamoto
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| From | Geert Uytterhoeven <geert@linux-m68k.org> |
|---|---|
| Date | 2017-05-15 16:30 +0200 |
| Message-ID | <tHpay-Ra-13@gated-at.bofh.it> |
| In reply to | #1641722 |
Hi Sakamoto-san,
On Mon, May 15, 2017 at 4:07 PM, Takashi Sakamoto
<o-takashi@sakamocchi.jp> wrote:
> On May 15 2017 17:19, Geert Uytterhoeven wrote:
>> Obviously the intention was to put a limit on the maximum number of
>> operations. However, for this to work, the check should be
>> "&& trials++ < 5", not "|| trials++ < 5".
>>
>> Fixes: 35efa5c489de63a9 ("ALSA: firewire-tascam: add streaming
>> functionality")
>> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
>> ---
>> Compile-tested only.
>>
>> Triggered by a false-positive warning from gcc-4.1.2:
>>
>> warning: ‘err’ may be used uninitialized in this function
>> ---
>> sound/firewire/tascam/tascam-stream.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/sound/firewire/tascam/tascam-stream.c
>> b/sound/firewire/tascam/tascam-stream.c
>> index f1657a4e0621ef49..e433b92ac6904db5 100644
>> --- a/sound/firewire/tascam/tascam-stream.c
>> +++ b/sound/firewire/tascam/tascam-stream.c
>> @@ -84,7 +84,7 @@ int snd_tscm_stream_get_rate(struct snd_tscm *tscm,
>> unsigned int *rate)
>> unsigned int trials = 0;
>> int err;
>>
>> - while (data == 0x0 || trials++ < 5) {
>> + while (data == 0x0 && trials++ < 5) {
>> err = get_clock(tscm, &data);
>> if (err < 0)
>> return err;
>
> Yep. It looks a bug.
>
> ...However, removal of the bug causes issue that the driver fails to start a
> pair of capture/playback PCM substream when application requests them mostly
> the same time, like jackd process.
>
> I think I did apply the bug as a makeshift workaround, then forgot itself
> when developing the driver... I'd like to have a bit time for further
> investigation, then post my fix in this development period.
Probably you need a small delay in the loop?
Why else do you #include <linux/delay.h>? ;-)
> Please let me keep this patch pending.
OK.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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| From | Takashi Sakamoto <o-takashi@sakamocchi.jp> |
|---|---|
| Date | 2017-05-15 16:50 +0200 |
| Subject | Re: [PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in snd_tscm_stream_get_rate() |
| Message-ID | <tHptU-XY-9@gated-at.bofh.it> |
| In reply to | #1641741 |
On May 15 2017 23:22, Geert Uytterhoeven wrote:
>>> diff --git a/sound/firewire/tascam/tascam-stream.c
>>> b/sound/firewire/tascam/tascam-stream.c
>>> index f1657a4e0621ef49..e433b92ac6904db5 100644
>>> --- a/sound/firewire/tascam/tascam-stream.c
>>> +++ b/sound/firewire/tascam/tascam-stream.c
>>> @@ -84,7 +84,7 @@ int snd_tscm_stream_get_rate(struct snd_tscm *tscm,
>>> unsigned int *rate)
>>> unsigned int trials = 0;
>>> int err;
>>>
>>> - while (data == 0x0 || trials++ < 5) {
>>> + while (data == 0x0 && trials++ < 5) {
>>> err = get_clock(tscm, &data);
>>> if (err < 0)
>>> return err;
>>
>> Yep. It looks a bug.
>>
>> ...However, removal of the bug causes issue that the driver fails to start a
>> pair of capture/playback PCM substream when application requests them mostly
>> the same time, like jackd process.
>>
>> I think I did apply the bug as a makeshift workaround, then forgot itself
>> when developing the driver... I'd like to have a bit time for further
>> investigation, then post my fix in this development period.
>
> Probably you need a small delay in the loop?
> Why else do you #include <linux/delay.h>? ;-)
I know PDI1394L40 (link layer) has quirks inconvenient to us.
Furthermore, the behaviour of on-board FPGAs with unique firmwares are
in black boxes to me.
I prefer deliberate approach for this kind of work, reverse engineering.
Regards
Takashi Sakamoto
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