Re: [PATCH] drm/dp/mst: dump branch OUI in debugfs

[Thierry Reding <thierry.reding@gmail.com>]

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On Tue, Jul 14, 2015 at 11:34:39AM +1000, Dave Airlie wrote:
> From: Dave Airlie <airlied@redhat.com>
> 
> It appears some MST docks are worse than other, but the only
> way to know is to see the sw revisions in here, so dump
> the branch OUI so we can look at the sw revision.
> 
> Signed-off-by: Dave Airlie <airlied@redhat.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 8a3bfcd..e17a639 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2657,6 +2657,11 @@ void drm_dp_mst_dump_topology(struct seq_file *m,
>  			seq_printf(m, "%02x ", buf[i]);
>  		seq_printf(m, "\n");
>  
> +		ret = drm_dp_dpcd_read(mgr->aux, DP_BRANCH_OUI, buf, DP_RECEIVER_CAP_SIZE);

According to the specification, the OUI is 24-bit, whereas the receiver
capability field is 15 bytes (well, at least that is the value defined
for DP_RECEIVER_CAP_SIZE)...

> +		seq_printf(m, "branch oui: ");
> +		for (i = 0; i < DP_RECEIVER_CAP_SIZE; i++)
> +			seq_printf(m, "%02x ", buf[i]);
> +		seq_printf(m, "\n");

So this will really dump out more than just the OUI. Perhaps it'd be
worth splitting that up further? 0x503 to 0x508 is an identification
string and displaying it as string would presumably be more useful than
the hexdump equivalent. Similarly 0x509 is a hardware revision and
0x50a/0x50b the firmware major/minor version, which might be more
readable in an idiomatic format (X.Y).

Thierry

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