From: Lino Sanfilippo <LinoSanfilippo@gmx.de>
To: Sean Young <sean@mess.org>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.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: Sat, 5 Dec 2020 00:16:01 +0100 [thread overview]
Message-ID: <e4a124a8-0905-4504-62e0-a809163775fe@gmx.de> (raw)
In-Reply-To: <20201204084417.GA2154@gofer.mess.org>
Hi Sean,
On 04.12.20 at 09:44, Sean Young wrote:
>> 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;
>
> Rather than doing another 64 bit division which is expensive (esp on 32 bit
> kernels), you could assign to u64 and check:
>
> if (value < PERIOD || value > U32_MAX)
> return -EINVAL;
>
Sound reasonable, I will adjust this.
>
> There was a problem where the carrier is incorrect for some IR hardware
> which uses a carrier of 455kHz. With periods that small, rounding errors
> do really matter and rounding down might cause problems.
>
> A policy of rounding down the carrier is not the right thing to do
> for pwm-ir-tx, and such a change will probably break pwm-ir-tx in some
> edge cases.
>
Thanks for this background information.
Regards,
Lino
next prev parent reply other threads:[~2020-12-04 23:18 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 [this message]
2020-12-04 11:21 ` Uwe Kleine-König
2020-12-04 11:40 ` Sean Young
2020-12-04 21:55 ` Uwe Kleine-König
2020-12-04 22:44 ` Sean Young
2020-12-04 23:25 ` Lino Sanfilippo
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