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SubjectRe: [RFC, PATCH] HSI: cmt_speech: fix timestamp interface
Hi Arnd,

[CC'd Kai's new mail address]

On Fri, Apr 10, 2015 at 01:59:19PM +0200, Arnd Bergmann wrote:
> The user interface for timestamps in the new cms_speech
> driver is broken in multiple ways:

ow :( Thanks for the report.

> - The layout is incompatible between 32-bit and 64-bit user
> space, because of the size differences in 'struct timespec'.
> This means that the driver can not work when used with 32-bit
> user space on a 64-bit kernel.
>
> - As there are plans to change 32-bit user space to use
> a 64-bit time_t type in the future, it will also be
> incompatible with new 32-bit user space.
>
> As the driver is not yet widely used, now would be a good time
> to change it to just use a 64-bit nanosecond value, which also
> happens to be more efficient. In order to make the layout
> non-ambiguous, we have to also add extra padding so the 64-bit
> value is naturally aligned.
>
> The change requires the respective update to user space tools
> using it. If that is for some reason not possible any more,
> another solution would be to replace the timespec structure
> with two __u32 values to avoid incompatibilities later.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

I think updating to two __u32 values is the better solution here.
While the driver is new in the mainline kernel it has been used
for multiple years downstream in the Maemo/MeeGo/Mer communities
and I would prefer to keep userspace compatibility.

-- Sebastian

> diff --git a/drivers/hsi/clients/cmt_speech.c b/drivers/hsi/clients/cmt_speech.c
> index 4983529a9c6c..568dbc117f2e 100644
> --- a/drivers/hsi/clients/cmt_speech.c
> +++ b/drivers/hsi/clients/cmt_speech.c
> @@ -451,9 +451,7 @@ static void cs_hsi_read_on_control_complete(struct hsi_msg *msg)
> dev_dbg(&hi->cl->device, "Read on control: %08X\n", cmd);
> cs_release_cmd(msg);
> if (hi->flags & CS_FEAT_TSTAMP_RX_CTRL) {
> - struct timespec *tstamp =
> - &hi->mmap_cfg->tstamp_rx_ctrl;
> - do_posix_clock_monotonic_gettime(tstamp);
> + hi->mmap_cfg->tstamp_rx_ctrl = ktime_get_ns();
> }
> spin_unlock(&hi->lock);
>
> diff --git a/include/uapi/linux/hsi/cs-protocol.h b/include/uapi/linux/hsi/cs-protocol.h
> index 4957bba57cbe..fce633c7c649 100644
> --- a/include/uapi/linux/hsi/cs-protocol.h
> +++ b/include/uapi/linux/hsi/cs-protocol.h
> @@ -90,12 +90,12 @@ struct cs_mmap_config_block {
> __u32 tx_offsets[CS_MAX_BUFFERS];
> __u32 rx_ptr;
> __u32 rx_ptr_boundary;
> - __u32 reserved3[2];
> + __u32 reserved3[3];
> /*
> * if enabled with CS_FEAT_TSTAMP_RX_CTRL, monotonic
> * timestamp taken when the last control command was received
> */
> - struct timespec tstamp_rx_ctrl;
> + __u64 tstamp_rx_ctrl;
> };
>
> #define CS_IO_MAGIC 'C'
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