From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Alex Elder <elder@ieee.org>
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Subject: Re: [PATCH v5 040/111] pwm: Provide devm_pwmchip_alloc() function
Date: Fri, 26 Jan 2024 18:10:38 +0100 [thread overview]
Message-ID: <zjt3r6z5ilpffh26qidwp3axpnvfkwcrwanrtjjm2kscpdovuz@ppcrdlhmqiqq> (raw)
In-Reply-To: <db05fb6a-2ea5-4e00-ac03-adc1897d96de@ieee.org>
[-- Attachment #1: Type: text/plain, Size: 1836 bytes --]
Hello Alex,
On Fri, Jan 26, 2024 at 08:56:33AM -0600, Alex Elder wrote:
> On 1/25/24 6:09 AM, Uwe Kleine-König wrote:
> > This function allocates a struct pwm_chip and driver data. Compared to
> > the status quo the split into pwm_chip and driver data is new, otherwise
> > it doesn't change anything relevant (yet).
> >
> > The intention is that after all drivers are switched to use this
> > allocation function, its possible to add a struct device to struct
> > pwm_chip to properly track the latter's lifetime without touching all
> > drivers again. Proper lifetime tracking is a necessary precondition to
> > introduce character device support for PWMs (that implements atomic
> > setting and doesn't suffer from the sysfs overhead of the /sys/class/pwm
> > userspace support).
> >
> > The new function pwmchip_priv() (obviously?) only works for chips
> > allocated with devm_pwmchip_alloc().
>
> I think this looks good. Two questions:
> - Should you explicitly align the private data? Or do you believe
> the default alignment (currently pointer size aligned) is adequate?
I'm not aware of a requirement for a higher order alignment (but I might
well miss something). I did my tests on arm, nothing exploded there.
Maybe the conservative approach of asserting the same alignment as
kmalloc would be a good idea. I'll think and research about that.
iio uses ARCH_DMA_MINALIGN, net uses 32 (NETDEV_ALIGN).
> - Is there a non-devres version of the allocation function?
Patch #109 introduces a non-devres variant. As it's not used it's a
static function though. Can easily be changed is a use case pops up.
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:[~2024-01-26 17:12 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-25 12:08 [PATCH v5 000/111] pwm: Improve lifetime tracking for pwm_chips Uwe Kleine-König
2024-01-25 12:08 ` [PATCH v5 003/111] pwm: Provide a macro to get the parent device of a given chip Uwe Kleine-König
2024-01-25 14:14 ` AngeloGioacchino Del Regno
2024-01-25 19:32 ` Florian Fainelli
2024-01-25 20:29 ` Uwe Kleine-König
2024-01-25 20:54 ` Uwe Kleine-König
2024-01-25 12:08 ` [PATCH v5 031/111] pwm: sun4i: Make use of pwmchip_parent() macro Uwe Kleine-König
2024-01-25 12:09 ` [PATCH v5 039/111] pwm: Provide wrappers for storing and getting driver private data Uwe Kleine-König
2024-01-25 14:13 ` AngeloGioacchino Del Regno
2024-01-25 12:09 ` [PATCH v5 040/111] pwm: Provide devm_pwmchip_alloc() function Uwe Kleine-König
2024-01-26 14:56 ` Alex Elder
2024-01-26 17:10 ` Uwe Kleine-König [this message]
2024-01-25 12:09 ` [PATCH v5 094/111] pwm: sun4i: Make use of " Uwe Kleine-König
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