From: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Jiri Slaby <jirislaby@kernel.org>,
Vinicius Pedrosa <vinicius.eduardo.pedrosa@gmail.com>,
linux-serial <linux-serial@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org,
devicetree@vger.kernel.org, LKML <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 14:50:53 +0300 (EEST) [thread overview]
Message-ID: <09812a6a-dd0d-9c47-e1ad-5220f1954648@linux.intel.com> (raw)
In-Reply-To: <atcm2zqDs1P_EDr0@ashevche-desk.local>
On Tue, 20 Oct 2026, Andy Shevchenko wrote:
> On Tue, Oct 20, 2026 at 08:11:06AM +0200, Jiri Slaby wrote:
> > On 19. 10. 26, 22:06, Vinicius Pedrosa wrote:
>
> ...
>
> > > - 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))
> > ?
>
> Yes, and since we check for reg to be "not zero", this will work the rest.
For is_power_of_2(), 0 is not a power of two. And it also wouldn't make
sense to have zero bits in the bit field as it's same as no bit field so
using just is_power_of_2() should be enough.
It could be that's what Andy meant, but the wording left too much room
for interpretation.
--
i.
next prev parent reply other threads:[~2026-10-20 11:51 UTC|newest]
Thread overview: 18+ 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 20:26 ` sashiko-bot
2026-10-20 8:30 ` Andy Shevchenko
2026-10-20 8:51 ` Andy Shevchenko
2026-10-20 10:47 ` Vinicius Pedrosa
2026-10-19 20:06 ` [PATCH v2 2/4] serial: 8250_dw: Only accept a contiguous DLF readback Vinicius Pedrosa
2026-10-19 20:24 ` sashiko-bot
2026-10-20 6:11 ` Jiri Slaby
2026-10-20 8:31 ` Andy Shevchenko
2026-10-20 11:50 ` Ilpo Järvinen [this message]
2026-10-20 12:27 ` Vinicius Pedrosa
2026-10-20 13:02 ` Ilpo Järvinen
2026-10-20 10:47 ` Vinicius Pedrosa
2026-10-19 20:06 ` [PATCH v2 3/4] dt-bindings: serial: snps-dw-apb-uart: Add Allwinner A733 Vinicius Pedrosa
2026-10-19 20:24 ` sashiko-bot
2026-10-19 20:06 ` [PATCH v2 4/4] serial: 8250_dw: Add Allwinner A733 UART Vinicius Pedrosa
2026-10-19 20:24 ` sashiko-bot
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