Re: [PATCH 2/2] serial: tegra: Fix overflow in tegra_check_rate_in_range()

[Svyatoslav Ryhel]

пн, 26 жовт. 2026 р. о 00:50 Patrick Fischer via B4 Relay
<devnull+admin.tsv-stahl-riesa.de@xxxxxxxxxx> пише:
>
> From: Patrick Fischer <admin@xxxxxxxxxxxxxxxxxx>
>
> tegra_check_rate_in_range() calculates the deviation of the configured
> from the required clock rate as (configured_rate - required_rate) *
> 10000 in a long, which is only 32 bits wide on 32-bit ARM. This
> overflows as soon as the two rates differ by more than about 214.7 kHz,
> so the check lets through exactly the large deviations it is meant to
> catch.
>
> On the Tegra Note 7 (Tegra114) the Bluetooth UART ran at 45.33 MHz
> instead of 48 MHz at 3 Mbaud (-5.6 %, see the previous patch). The
> check calculated -0.18 % and let it pass, although the limit is 4 %.
>
> Do the multiplication in 64 bits.
>
> Tested on the Tegra Note 7 with a tolerance of -500 for 1 to 4 Mbaud,
> which gives 45.33 MHz at 3 Mbaud: the driver now logs
> "configured baud rate is out of range by -555" and does not apply the
> rate. With the tolerance of 136 (48.00 MHz) it logs nothing.
>
> 64-bit platforms are not affected.
>
> Fixes: d781ec21bae6 ("serial: tegra: report clk rate errors")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Patrick Fischer <admin@xxxxxxxxxxxxxxxxxx>
> ---
>  drivers/tty/serial/serial-tegra.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>

Tested-by: Svyatoslav Ryhel <clamor95@xxxxxxxxx> # Tegratab (P1988) and LG P895
Reviewed-by: Svyatoslav Ryhel <clamor95@xxxxxxxxx>