Re: [PATCH] thunderbolt: debugfs: Don't stop reading SB registers if just one fails

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 4/10/26 4:29 PM, Konrad Dybcio wrote:
> On 4/9/26 4:32 PM, Mika Westerberg wrote:
>> On Thu, Apr 09, 2026 at 02:59:22PM +0200, Konrad Dybcio wrote:
>>> On 4/9/26 2:04 PM, Mika Westerberg wrote:
> 
> [...]
> 
>>>> I assume you have tested this on a hardware that supports this too, right?
>>>
>>> Hardware that exposes that register this does not exercise the altered
>>> code path.
>>
>> Well it may happen now that previously we got -EIO from some other register
>> and we stopped there, now this changes and we actually continue reading so
>> this definitely should be tested.
> 
> The only register before USB4_SB_GEN4_TXFFE that isn't in-spec for
> both retimers in v1.0 and v2.0 is USB4_SB_LRD_TUNING (0x07). The PS8830
> interestingly reports all zeroes (not a bounce).
> 
> The registers following USB4_SB_GEN4_TXFFE in the array are
> USB4_SB_VERSION and USB4_SB_DATA. The former is not accessed anywhere
> else in the code, at first glance. The latter is, during NVM r/w and
> in margining ops, which have definitely been in use for a long time.
> 
> Plus both of them are the v1.0 spec. The USB4_SB_GEN4_TXFFE specifically
> isn't (the retimer supplement pdf lists it as Rsvd, the main spec pdf
> omits it in the SB register table), as it wasn't previously useful (since
> Gen4 came about in v2.0).
> 
> 
> I don't think there's an easy way to limit the reading of this register
> since the bit indicating Gen4 capability is in USB4_SB_LINK_CONF (0x0c),
> which is Rsvd on retimers regardless of the spec revision. A connected
> port could easily have higher/lower capabilities, too.

Checked again, the USB4_SB_FW_VERSION (0x02) register's lowest 8 bytes
are 0/1 for retimers implementing USB4v1 and 2 for v2, so we may go this
path too

Konrad