linux-kernel - Re: [PATCH] ARC: HSDK: improve reset driver

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Date:   Fri, 14 Sep 2018 12:38:13 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
Cc:     linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Alexey Brodkin <Alexey.Brodkin@...opsys.com>
Subject: Re: [PATCH] ARC: HSDK: improve reset driver

Hi Eugeniy,

On Mon, 2018-08-27 at 17:38 +0300, Eugeniy Paltsev wrote:
> As for today HSDK reset driver implements only
> .reset() callback.
> 
> In case of driver which implements one of standard
> reset controller usage pattern
> (call *_deassert() in probe(), call *_assert() in remove())
> that leads to inoperability of this reset driver.
> 
> Improve HSDK reset driver by calling .reset() callback inside of
> .assert()/.deassert() callbacks to avoid each reset controller
> user adaptation for work with both reset methods
> (reset() and .assert()/.deassert() pair)
> 
> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
> ---
>  drivers/reset/reset-hsdk.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/reset/reset-hsdk.c b/drivers/reset/reset-hsdk.c
> index 8bce391c6943..1fd91df91343 100644
> --- a/drivers/reset/reset-hsdk.c
> +++ b/drivers/reset/reset-hsdk.c
> @@ -86,6 +86,8 @@ static int hsdk_reset_reset(struct reset_controller_dev *rcdev,
>  
>  static const struct reset_control_ops hsdk_reset_ops = {
>  	.reset	= hsdk_reset_reset,
> +	.assert = hsdk_reset_reset,

This is incorrect for exclusive reset controls.
It will cause reset_control_assert() to return success for exclusive
reset controls, even though the .assert op failed to leave the reset
line asserted after the function returns.

While calling hsdk_reset_reset from .assert for shared reset controls
would be fine, I don't see how this is necessary of useful.
If a consumer driver requires the reset to be asserted upon remove(), it
must not request a shared reset control anyway, because with shared
reset controls other drivers may keep the reset line deasserted
indefinitely.

> +	.deassert = hsdk_reset_reset,

This should be fine. I wonder from time to time whether this should be
implemented in the core, in reset_control_deassert().

regards
Philipp