Re: [PATCH v2 2/2] serial: 8250_ingenic: Set UMR and UACR at probe

[sashiko-bot@kernel.org]

> Ingenic UARTs have two registers beyond the 16550's: UMR, the number of
> clocks a bit takes, and UACR, which adds one clock to chosen bits of a
> frame, for fractional baud rates. The JZ4725, JZ4740, JZ4755, JZ4760,
> X1000, X1830, X2000 and X1600 programming manuals all have them at 0x24
> and 0x28. The divisor the 8250 core computes assumes 16 clocks a bit and
> none added.
> 
> The driver never writes them, so a UART keeps whatever was there before.
> On a HiBy R1 (X1600) the vendor boot loader sets UMR to 8 on its console
> UART, and the vendor kernel had left 8 on UART0, which carries the
> Bluetooth chip: every rate came out doubled, and the chip never answered
> ("command 0xfc18 tx timeout" from hci_bcm). Their reset value, 0, which
> the X1000 and X1600 manuals call normal mode, does not work on the X1600
> either: with UMR at 0 the same command times out.
> 
> Set UMR to 16 and UACR to 0 at probe.
> 
> Tested on a HiBy R1: with UMR at 0 or 8 the BCM43430A1 on UART0 fails to
> set up; with this patch it comes up at 1.5 Mbaud and streams A2DP audio.
> 
> Signed-off-by: Olivier Louvignes <olivier@mgcrea.io>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261024220712.23250-1-olivier@mgcrea.io?part=2