Re: [PATCH v2] coresight: etm4x: return 0 instead of using local ret variable

[Shile Zhang]

On 2022/4/22 23:45, Mathieu Poirier wrote:
> On Fri, Apr 22, 2022 at 10:02:39AM +0800, Shile Zhang wrote:
> > The function etm4_remove_dev() always return 0, and the former function
> > etm4_remove has been changed to void in commit 3fd269e74f2fe ("amba: Make
> > the remove callback return void"). But now its changed back to int type
> > for some reason, which is different to the stable branch linux-5.10.y.
>
> Please spend time understanding why function etm4_remove_dev()'s return value
> has been changed back to an "int".  From there you will likely come to the
> conclusion that adding the above to the changelog doesn't make sense.

Sorry, I means "some reason" here actually I cannot find out why.

1. From the git log of the file 
`drivers/hwtracing/coresight/coresight-etm4x-core.c', only log of 
etm4_remove changes to void in commit 3fd269e74f2fe. no any log record 
when it change back to int.
2. from the commit 'git log --pretty="%h %ci %cn %s" 
drivers/hwtracing/coresight/coresight-etm4x-core.c'
...
b8336ad947e19 2021-02-04 17:00:32 +0100 Greg Kroah-Hartman coresight: 
etm4x: add AMBA id for Cortex-A55 and Cortex-A75
3fd269e74f2fe 2021-02-02 14:25:50 +0100 Uwe Kleine-König amba: Make the 
remove callback return void
...

The commit 'b8336ad947e19' does not change the etm4_remove:
https://github.com/torvalds/linux/commit/b8336ad947e1913b9bb5cdf4f54b687654160d42

But the different between the commit 'b8336ad947e19' and '3fd269e74f2fe' 
contains the changes of etm4_remove back to int, as following:
---
...
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c 
b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 82787cba537d3..8c4b0c46c8f32 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -1680,7 +1680,7 @@ static void clear_etmdrvdata(void *info)
        etmdrvdata[cpu] = NULL;
 }

-static void etm4_remove(struct amba_device *adev)
+static int etm4_remove(struct amba_device *adev)
 {
        struct etmv4_drvdata *drvdata = dev_get_drvdata(&adev->dev);

@@ -1703,6 +1703,8 @@ static void etm4_remove(struct amba_device *adev)
        cpus_read_unlock();

        coresight_unregister(drvdata->csdev);
+
+       return 0;
 }

 static const struct amba_id etm4_ids[] = {
@@ -1711,6 +1713,8 @@ static const struct amba_id etm4_ids[] = {
        CS_AMBA_ID(0x000bb95a),                 /* Cortex-A72 */
        CS_AMBA_ID(0x000bb959),                 /* Cortex-A73 */
        CS_AMBA_UCI_ID(0x000bb9da, uci_id_etm4),/* Cortex-A35 */
+       CS_AMBA_UCI_ID(0x000bbd05, uci_id_etm4),/* Cortex-A55 */
+       CS_AMBA_UCI_ID(0x000bbd0a, uci_id_etm4),/* Cortex-A75 */
        CS_AMBA_UCI_ID(0x000bbd0c, uci_id_etm4),/* Neoverse N1 */
        CS_AMBA_UCI_ID(0x000f0205, uci_id_etm4),/* Qualcomm Kryo */
        CS_AMBA_UCI_ID(0x000f0211, uci_id_etm4),/* Qualcomm Kryo */
...
---

I really don't know how to check which commit change it back.
Could you please help to give me some guidance?

Thanks!


> > Just let it return void and return 0 directly in it's caller function
> > etm4_remove_platform_dev.
>
> The only rational for this patch is that etm4_remove_dev() always returns '0'.
> And even if it was to return anything else, the return value it not checked.
> And even if the return value was checked, there is nothing to do about an error
> condition since the driver is being removed.
>
> > Signed-off-by: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx>
> > ---
> > v2: re-work the commit log from Mathieu's suggestion.
> > v1: https://lore.kernel.org/linux-arm-kernel/20220421164217.GB1596562@p14s/T/
> > ---
> >   drivers/hwtracing/coresight/coresight-etm4x-core.c | 11 +++++------
> >   1 file changed, 5 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > index 7f416a12000eb..141f8209a152a 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > @@ -2104,7 +2104,7 @@ static void clear_etmdrvdata(void *info)
> >   	etmdrvdata[cpu] = NULL;
> >   }
> >   
> > -static int __exit etm4_remove_dev(struct etmv4_drvdata *drvdata)
> > +static void __exit etm4_remove_dev(struct etmv4_drvdata *drvdata)
> >   {
> >   	etm_perf_symlink(drvdata->csdev, false);
> >   	/*
> > @@ -2125,8 +2125,6 @@ static int __exit etm4_remove_dev(struct etmv4_drvdata *drvdata)
> >   
> >   	cscfg_unregister_csdev(drvdata->csdev);
> >   	coresight_unregister(drvdata->csdev);
> > -
> > -	return 0;
> >   }
> >   
> >   static void __exit etm4_remove_amba(struct amba_device *adev)
> > @@ -2139,13 +2137,14 @@ static void __exit etm4_remove_amba(struct amba_device *adev)
> >   
> >   static int __exit etm4_remove_platform_dev(struct platform_device *pdev)
> >   {
> > -	int ret = 0;
> >   	struct etmv4_drvdata *drvdata = dev_get_drvdata(&pdev->dev);
> >   
> >   	if (drvdata)
> > -		ret = etm4_remove_dev(drvdata);
> > +		etm4_remove_dev(drvdata);
> > +
> >   	pm_runtime_disable(&pdev->dev);
> > -	return ret;
> > +
> > +	return 0;
> >   }
> >   
> >   static const struct amba_id etm4_ids[] = {
> > --
> > 2.33.0.rc2