linux-kernel - Re: [PATCH] drm/imagination: Fix timestamps in firmware traces

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Message-ID: <41383f9a-ff72-4911-aa2d-00702a8d62eb@imgtec.com>
Date: Mon, 3 Mar 2025 12:15:21 +0000
From: Matt Coster <Matt.Coster@...tec.com>
To: Alessio Belle <Alessio.Belle@...tec.com>
CC: Frank Binns <Frank.Binns@...tec.com>,
        Alexandru Dadu
	<Alexandru.Dadu@...tec.com>,
        Maarten Lankhorst
	<maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/imagination: Fix timestamps in firmware traces

On 21/02/2025 10:49, Alessio Belle wrote:
> When firmware traces are enabled, the firmware dumps 48-bit timestamps
> for each trace as two 32-bit values, highest 32 bits (of which only 16
> useful) first.
> 
> The driver was reassembling them the other way round i.e. interpreting
> the first value in memory as the lowest 32 bits, and the second value
> as the highest 32 bits (then truncated to 16 bits).
> 
> Due to this, firmware trace dumps showed very large timestamps even for
> traces recorded shortly after GPU boot. The timestamps in these dumps
> would also sometimes jump backwards because of the truncation.
> 
> Example trace dumped after loading the powervr module and enabling
> firmware traces, where each line is commented with the timestamp value
> in hexadecimal to better show both issues:
> 
> [93540092739584] : Host Sync Partition marker: 1    // 0x551300000000
> [28419798597632] : GPU units deinit                 // 0x19d900000000
> [28548647616512] : GPU deinit                       // 0x19f700000000
> 
> Update logic to reassemble the timestamps halves in the correct order.
> 
> Fixes: cb56cd610866 ("drm/imagination: Add firmware trace to debugfs")
> Signed-off-by: Alessio Belle <alessio.belle@...tec.com>

Reviewed-by: Matt Coster <matt.coster@...tec.com>

Cheers,
Matt

> ---
>  drivers/gpu/drm/imagination/pvr_fw_trace.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/imagination/pvr_fw_trace.c b/drivers/gpu/drm/imagination/pvr_fw_trace.c
> index 73707daa4e52d13fd1388cb2e9feff0aea109620..5dbb636d7d4ffeea2253ea58e817710979f90cf0 100644
> --- a/drivers/gpu/drm/imagination/pvr_fw_trace.c
> +++ b/drivers/gpu/drm/imagination/pvr_fw_trace.c
> @@ -333,8 +333,8 @@ static int fw_trace_seq_show(struct seq_file *s, void *v)
>         if (sf_id == ROGUE_FW_SF_LAST)
>                 return -EINVAL;
> 
> -       timestamp = read_fw_trace(trace_seq_data, 1) |
> -               ((u64)read_fw_trace(trace_seq_data, 2) << 32);
> +       timestamp = ((u64)read_fw_trace(trace_seq_data, 1) << 32) |
> +               read_fw_trace(trace_seq_data, 2);
>         timestamp = (timestamp & ~ROGUE_FWT_TIMESTAMP_TIME_CLRMSK) >>
>                 ROGUE_FWT_TIMESTAMP_TIME_SHIFT;
> 
> 
> ---
> base-commit: 938fbb16aba8f7b88e0fdcf56f315a5bbad41aad
> change-id: 20250220-fix-fw-trace-timestamps-15d70bb2d93d
> 
> Best regards,
> --
> Alessio Belle <alessio.belle@...tec.com>
> 


-- 
Matt Coster
E: matt.coster@...tec.com


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