Re: [PATCH v2] usb: dwc3: Update nominal max votes for qcom usb

[sashiko-bot@kernel.org]

> Increase the nominal max USB memory bandwidth vote to let DDR scale
> higher within its nominal corner, fixing glitches seen during
> simultaneous USB audio use cases.
> 
> USB_MEMORY_PEAK_SS_BW is raised from 2500 MB/s to 4500 MB/s (+2000
> MB/s, ~1.8x). This ICC vote does not by itself determine DDR
> frequency; the vote-to-frequency mapping is platform-specific and
> comes from each target's interconnect/OPP table. On the tested
> targets, the old vote kept DDR pinned at 1 GHz within the nominal
> corner, even though DDR can run at 1.5 GHz (+50%) within the same
> corner. At 1 GHz, glitches were observed during multiple concurrent
> USB audio use cases.
> 
> Tested internally on RB3, RB4, RB8, Shikra, and other KLM targets.
> With the updated vote, DDR is allowed to run at the higher nominal
> frequency, and the following were measured (not merely projected):
> 
> - USB memory throughput: 125 MB/s -> 145 MB/s (+16%)
> - RTD-USBC audio latency: 17.9 ms -> 16.6 ms (-7.3%)
> 
> RTD-USBC is the round-trip audio latency measured over a USB-C audio
> path; lower is better. Note the +50% DDR frequency headroom does not
> map linearly to the +16% throughput gain, since throughput is also
> bounded by other factors along the USB/DDR path; the frequency
> increase is necessary but not sufficient to explain the full gain on
> its own.
> 
> Signed-off-by: Akash Kumar <akash.kumar@oss.qualcomm.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261105100626.2003771-1-akash.kumar@oss.qualcomm.com?part=1