linux-kernel - Re: [PATCH] coresight: stm: return error code instead of zero in .packet() to avoid dead loop

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Date:   Fri, 9 Sep 2016 09:36:12 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Chunyan Zhang <zhang.chunyan@...aro.org>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Lyra Zhang <zhang.lyra@...il.com>
Subject: Re: [PATCH] coresight: stm: return error code instead of zero in
 .packet() to avoid dead loop

On 9 September 2016 at 04:18, Chunyan Zhang <zhang.chunyan@...aro.org> wrote:
> In STM framework driver, the trace data writing loop would keep running
> until it received a negative return value or the whole trace packet has
> been written to STM device.  So if the .packet() of STM device always
> returns zero since the device is not enabled or the parameter isn't
> supported, STM framework driver will stall into a dead loop.
>
> Returning -EACCES (Permission denied) in .packet() if the device is
> disabled makes more sense, and this is the same for returning -EINVAL
> if the channel passed into is not supported.
>
> Signed-off-by: Chunyan Zhang <zhang.chunyan@...aro.org>
> ---
>  drivers/hwtracing/coresight/coresight-stm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-stm.c b/drivers/hwtracing/coresight/coresight-stm.c
> index 73be58a..6291ce1 100644
> --- a/drivers/hwtracing/coresight/coresight-stm.c
> +++ b/drivers/hwtracing/coresight/coresight-stm.c
> @@ -399,10 +399,10 @@ static ssize_t stm_generic_packet(struct stm_data *stm_data,
>                                                    struct stm_drvdata, stm);
>
>         if (!(drvdata && local_read(&drvdata->mode)))
> -               return 0;
> +               return -EACCES;
>
>         if (channel >= drvdata->numsp)
> -               return 0;
> +               return -EINVAL;
>
>         ch_addr = (unsigned long)stm_channel_addr(drvdata, channel);
>
> --
> 2.7.4
>

Applied, but I had to change the title to "coresight: stm: return
error code instead of zero in .packet()" as the previous one exceeded
80 characters.

Thanks,
Mathieu