On Fri, 25 Apr 2008, Takashi Iwai wrote:
> At Fri, 25 Apr 2008 10:23:51 +0200 (CEST),
> Jaroslav Kysela wrote:
> >
> > On Fri, 25 Apr 2008, Takashi Iwai wrote:
> >
> > > At Fri, 25 Apr 2008 09:35:47 +0200 (CEST),
> > > Jaroslav Kysela wrote:
> > > >
> > > > On Fri, 25 Apr 2008, Takashi Iwai wrote:
> > > >
> > > > > > Sure. I applied the simple 'void *device_private_data' patch, because
> > > > > > current usage request is really trivial. We can implement complex code to
> > > > > > handle data for multiple "extra" devices on AC97 bus later.
> > > > >
> > > > > Actually, it's not "used" yet. The ucb1000 reads the data but no one
> > > > > stores yet. And, if its usage request is trivial, we should use "int
> > > >
> > > > Yes, I hope that the appropriate initialization code will be added to SoC
> > > > drivers, too.
> > > >
> > > > > irq" as in the original patch instead of void data and cast.
> > > >
> > > > But other SoC (or other) drivers might want to pass to extra devices on
> > > > AC97 bus something different or more complex. Mark Brown already noted
> > > > that. I would keep it as 'void *'.
> > >
> > > That's the very problem I've been trying to point out.
> > > The void pointer is good if the same driver assigns and casts. But,
> > > in this case, the allocator and the receiver are different. Thus,
> > > there is no guarantee that the data type is what you want. OTOH, if
> > > it's "int irq", this is crystal clear.
> > >
> > > So, in short:
> > >
> > > - if only one device needs such data, it should be a strong type like
> > > "int irq" anyway -- no extra need to cast to void pointer
> > > - if multiple devices need such a pass-away mechanism, then they can
> > > crash because you have no data type check. The void pointer is
> > > dangerous for multiple devices.
> >
> > I see. In this case, I would propose to add a 32-bit "magic" at the
> > start of 'void *' data. How about this modification:
>
> The magic number sounds OK, but funky cast to integer pointer is bad.
> If you have a long or a pointer after int, you can have an alignment
> problem on 64bit archs, for example.
Not really. First 32-bit word has offset 0 and next 64-bit word has offset
8 on x86-64. So alignment is OK.
Anyway, I agree that with a struct, code is more readable without hidden
things. Also, drivers can define own struct with magic member as first.
Here is corrected patch:
diff -r e2ff47e8771b include/ac97_codec.h
--- a/include/ac97_codec.h Fri Apr 25 08:29:05 2008 +0200
+++ b/include/ac97_codec.h Fri Apr 25 11:43:11 2008 +0200
@@ -407,6 +407,9 @@
#define AC97_RATES_MIC_ADC 4
#define AC97_RATES_SPDIF 5
+/* device private data magic number */
+#define AC97_PDEVMAGIC_UIRQ 0x55495251 /* in ASCII: UIRQ, for UCB1400 */
+
/*
*
*/
@@ -470,6 +473,15 @@ struct snd_ac97_template {
const struct snd_ac97_res_table *res_table; /* static resolution */
};
+struct ac97_pdevdata {
+ unsigned int magic; /* see AC97_PDEVMAGIC */
+ union {
+ int ivalue;
+ long lvalue;
+ void *pvalue;
+ } u;
+};
+
struct snd_ac97 {
/* -- lowlevel (hardware) driver specific -- */
struct snd_ac97_build_ops * build_ops;
@@ -478,7 +490,7 @@ struct snd_ac97 {
/* This field is used by device drivers which serve devices which are
* attached to the AC97 bus.
*/
- void *device_private_data;
+ struct ac97_pdevdata *device_private_data;
/* --- */
struct snd_ac97_bus *bus;
struct pci_dev *pci; /* assigned PCI device - used for quirks */
@@ -545,6 +557,11 @@ static inline int ac97_can_spdif(struct
static inline int ac97_can_spdif(struct snd_ac97 * ac97)
{
return (ac97->ext_id & AC97_EI_SPDIF) != 0;
+}
+static inline int ac97_check_pdevdata_magic(struct snd_ac97 * ac97, unsigned int magic)
+{
+ return ac97->device_private_data &&
+ ac97->device_private_data->magic == magic;
}
/* functions */
diff -r e2ff47e8771b kernel/drivers/input/touchscreen/ucb1400_ts.c
--- a/kernel/drivers/input/touchscreen/ucb1400_ts.c Fri Apr 25 08:29:05 2008 +0200
+++ b/kernel/drivers/input/touchscreen/ucb1400_ts.c Fri Apr 25 11:43:11 2008 +0200
@@ -492,14 +492,14 @@ static int ucb1400_ts_probe(struct devic
goto err_free_devs;
}
- if (!ucb->ac97->device_private_data) {
+ if (!ac97_check_pdevdata_magic(usb->ac97, AC97_PDEVMAGIC_UIRQ)) {
error = ucb1400_detect_irq(ucb);
if (error) {
printk(KERN_ERR "UCB1400: IRQ probe failed\n");
goto err_free_devs;
}
} else {
- ucb->irq = (int) ucb->ac97->device_private_data;
+ ucb->irq = ucb->ac97->device_private_data->u.ivalue;
}
error = request_irq(ucb->irq, ucb1400_hard_irq, IRQF_TRIGGER_RISING,
-----
Jaroslav Kysela <perex@xxxxxxxx>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.
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