From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Sean Young <sean@mess.org>
Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de>,
thierry.reding@gmail.com, lee.jones@linaro.org,
nsaenzjulienne@suse.de, f.fainelli@gmail.com, rjui@broadcom.com,
sbranden@broadcom.com, bcm-kernel-feedback-list@broadcom.com,
linux-pwm@vger.kernel.org, linux-rpi-kernel@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] pwm: bcm2835: Support apply function for atomic configuration
Date: Fri, 4 Dec 2020 22:55:25 +0100 [thread overview]
Message-ID: <20201204215525.uvjxlebth457aoj5@pengutronix.de> (raw)
In-Reply-To: <20201204114036.GB6547@gofer.mess.org>
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Hello Sean,
On Fri, Dec 04, 2020 at 11:40:36AM +0000, Sean Young wrote:
> On Fri, Dec 04, 2020 at 12:21:15PM +0100, Uwe Kleine-König wrote:
> > On Fri, Dec 04, 2020 at 12:42:15AM +0100, Lino Sanfilippo wrote:
> > > On 29.11.20 at 19:10, Uwe Kleine-König wrote:
> > > > You're storing an unsigned long long (i.e. 64 bits) in an u32. If
> > > > you are sure that this won't discard relevant bits, please explain
> > > > this in a comment for the cursory reader.
> > >
> > > What about an extra check then to make sure that the period has not been truncated,
> > > e.g:
> > >
> > > value = DIV_ROUND_CLOSEST_ULL(state->period, scaler);
> > >
> > > /* dont accept a period that is too small or has been truncated */
> > > if ((value < PERIOD_MIN) ||
> > > (value != DIV_ROUND_CLOSEST_ULL(state->period, scaler)))
> > > return -EINVAL;
> >
> > I'd make value an unsigned long long and check for > 0xffffffff instead
> > of repeating the (expensive) division. (Hmm, maybe the compiler is smart
> > enough to not actually repeat it, but still.)
>
> I wonder where you got that idea from.
I don't know how to honestly answer your question.
Which idea do you mean? That divisions are expensive? Or that compilers
might be smart? And do you consider it a good idea? Or do you disagree?
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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next prev parent reply other threads:[~2020-12-04 21:56 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <202011281128.54eLfMWr-lkp@intel.com>
2020-11-28 12:02 ` [PATCH v2] pwm: bcm2835: Support apply function for atomic configuration Lino Sanfilippo
2020-11-29 18:10 ` Uwe Kleine-König
2020-12-03 23:42 ` Lino Sanfilippo
2020-12-04 8:44 ` Sean Young
2020-12-04 8:58 ` Sean Young
2020-12-04 11:13 ` Uwe Kleine-König
2020-12-04 11:38 ` Sean Young
2020-12-04 23:28 ` Uwe Kleine-König
2020-12-05 17:34 ` Sean Young
2020-12-05 19:25 ` Uwe Kleine-König
2020-12-06 14:19 ` Sean Young
2020-12-07 8:16 ` Uwe Kleine-König
2020-12-07 9:43 ` Sean Young
2020-12-07 13:52 ` Uwe Kleine-König
2020-12-07 15:29 ` Thierry Reding
2020-12-07 21:46 ` Uwe Kleine-König
2020-12-07 18:18 ` Sean Young
2020-12-08 0:00 ` Lino Sanfilippo
2020-12-08 9:07 ` Uwe Kleine-König
2020-12-04 23:16 ` Lino Sanfilippo
2020-12-04 11:21 ` Uwe Kleine-König
2020-12-04 11:40 ` Sean Young
2020-12-04 21:55 ` Uwe Kleine-König [this message]
2020-12-04 22:44 ` Sean Young
2020-12-04 23:25 ` Lino Sanfilippo
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