lkml.org 
[lkml]   [2020]   [Oct]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] spi: imx: Revert "spi: imx: enable runtime pm support"
Date
Hi Sascha,

On Friday, 9 October 2020, 09:39:44 CEST, Sascha Hauer wrote:
> On Fri, Oct 09, 2020 at 06:27:38AM +0200, Christian Eggers wrote:
> > This reverts commit 525c9e5a32bd7951eae3f06d9d077fea51718a6c.
> >
> > If CONFIG_PM is disabled, the system completely freezes on probe as
> > nothing enables the clock of the SPI peripheral.
>
> Instead of reverting it, why not just fix it?
>
> Normally the device should be brought to active state manually in probe
> before pm_runtime takes over, then CONFIG_PM disabled doesn't hurt.
> Using pm_runtime to put the device to active state initially has the
> problem you describe.

prior introducing runtime pm for spi-imx, the clock was "manually" enabled and
disabled around each transfer (so the power usage should already have been
optimal). If we would manually enable the clock in probe() as you suggested,
for users without CONFIG_PM there would be a drawback compared with the
previous state (as the clock will always be on now).

What is the benefit of controlling the SPI clock with runtime PM instead of
doing it manually?

As I have no experience with runtime PM, hopefully somebody else can fix (or
revert) this.

@Clark: I forgot to put you on CC on my initial message. You can find the full
discussion here:
https://lore.kernel.org/patchwork/patch/1318736/

Best regards
Christian




\
 
 \ /
  Last update: 2020-10-12 13:01    [W:0.163 / U:2.116 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site