From: Jiri Slaby <jirislaby@kernel.org>
To: Vinicius Pedrosa <vinicius.eduardo.pedrosa@gmail.com>,
linux-serial@vger.kernel.org
Cc: gregkh@linuxfoundation.org, robh@kernel.org, krzk+dt@kernel.org,
conor+dt@kernel.org, andriy.shevchenko@linux.intel.com,
ilpo.jarvinen@linux.intel.com, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-sunxi@lists.linux.dev,
Andre Przywara <andre.przywara@arm.com>,
Chen-Yu Tsai <wens@kernel.org>,
Jernej Skrabec <jernej.skrabec@gmail.com>,
Samuel Holland <samuel@sholland.org>,
Enzo Adriano <enzo.adriano.code@gmail.com>
Subject: Re: [PATCH v2 2/4] serial: 8250_dw: Only accept a contiguous DLF readback
Date: Tue, 20 Oct 2026 08:11:06 +0200 [thread overview]
Message-ID: <d992e18d-31ab-4937-8780-9c9dc423082a@kernel.org> (raw)
In-Reply-To: <a79114e72d029732db6764935dde12aa5d497706.1792439398.git.vinicius.eduardo.pedrosa@gmail.com>
On 19. 10. 26, 22:06, Vinicius Pedrosa wrote:
> --- a/drivers/tty/serial/8250/8250_dwlib.c
> +++ b/drivers/tty/serial/8250/8250_dwlib.c
> @@ -225,7 +225,11 @@ void dw8250_setup_port(struct uart_port *p)
> reg = dw8250_readl_ext(p, DW_UART_DLF);
> dw8250_writel_ext(p, DW_UART_DLF, old_dlf);
>
> - if (reg) {
> + /*
> + * DLF is a bit field starting at bit 0, so a real one reads back as
> + * 2^n - 1. Any other value means this offset is something else.
> + */
> + if (reg && !(reg & (reg + 1))) {
Do I understand correctly, that this equivalent to:
if (is_power_of_2(reg + 1))
?
thanks,
--
js
suse labs
next prev parent reply other threads:[~2026-10-20 6:11 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-19 20:06 [PATCH v2 0/4] serial: 8250_dw: Allwinner A733 UART support Vinicius Pedrosa
2026-10-19 20:06 ` [PATCH v2 1/4] serial: 8250_dw: Keep the BUSY-safe divisor hook when DLF is present Vinicius Pedrosa
2026-10-19 20:06 ` [PATCH v2 2/4] serial: 8250_dw: Only accept a contiguous DLF readback Vinicius Pedrosa
2026-10-20 6:11 ` Jiri Slaby [this message]
2026-10-19 20:06 ` [PATCH v2 3/4] dt-bindings: serial: snps-dw-apb-uart: Add Allwinner A733 Vinicius Pedrosa
2026-10-19 20:06 ` [PATCH v2 4/4] serial: 8250_dw: Add Allwinner A733 UART Vinicius Pedrosa
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