From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Stefan Agner <stefan@agner.ch>
Cc: Lukasz Majewski <lukma@denx.de>,
Thierry Reding <thierry.reding@gmail.com>,
Sascha Hauer <s.hauer@pengutronix.de>,
linux-pwm@vger.kernel.org,
Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>,
linux-kernel@vger.kernel.org,
Lothar Wassmann <LW@karo-electronics.de>,
kernel@pengutronix.de, Fabio Estevam <fabio.estevam@nxp.com>,
Lukasz Majewski <l.majewski@majess.pl>
Subject: Re: [PATCH v4 07/11] pwm: imx: Provide atomic PWM support for i.MX PWMv2
Date: Tue, 10 Jan 2017 08:59:09 +0100 [thread overview]
Message-ID: <20170110085909.69b80820@bbrezillon> (raw)
In-Reply-To: <66893ecf40113ccd55569ca99be093f0@agner.ch>
On Mon, 09 Jan 2017 19:14:43 -0800
Stefan Agner <stefan@agner.ch> wrote:
> >>
> >> >
> >> > But, while reviewing your patch I realized this was actually unneeded
> >> > (see the explanation in my previous review).
> >> >
> >> > >
> >> > > Now it depends on cstate.enabled flag.
> >> > >
> >> > > So we end up with
> >> > >
> >> > > if (state.enabled && !cstate.enabled)
> >> > > clk_preapre_enable();
> >> >
> >> > Yep, and that's correct.
> >>
> >> And following patch:
> >> http://patchwork.ozlabs.org/patch/709510/
> >>
> >> address this issue.
> >
> > Yes, that was needed because the enable/disable path were not
> > separated, and we were unconditionally writing to the IP registers
> > even when the PWM was already disabled (which is probably the case
> > generating the fault reported by Stefan). This is not the case anymore,
> > but let's wait for Stefan to confirm this.
>
> With v4 as is, the kernel crashes/hangs on i.MX 7.
>
> The function imx_pwm_apply_v2 gets first called with state->enabled 0,
> cstate->enabled 0. This branches to else and leads to a register access
> with clocks disabled (and if that would succeed, also an unbalanced
> disable?...)
>
> With the proposed change plus the additional change in the else branch
> it works for me:
>
> @@ -192,19 +193,20 @@ static int imx_pwm_apply_v2(struct pwm_chip *chip,
> struct pwm_device *pwm,
> else
> period_cycles = 0;
>
> - ret = clk_prepare_enable(imx->clk_per);
> - if (ret)
> - return ret;
> -
> /*
> * Wait for a free FIFO slot if the PWM is already
> enabled, and
> * flush the FIFO if the PWM was disabled and is about
> to be
> * enabled.
> */
> - if (cstate.enabled)
> + if (cstate.enabled) {
> imx_pwm_wait_fifo_slot(chip, pwm);
> - else if (state->enabled)
> + } else if (state->enabled) {
> + ret = clk_prepare_enable(imx->clk_per);
> + if (ret)
> + return ret;
> +
> imx_pwm_sw_reset(chip);
> + }
>
> writel(duty_cycles, imx->mmio_base + MX3_PWMSAR);
> writel(period_cycles, imx->mmio_base + MX3_PWMPR);
> @@ -218,7 +220,7 @@ static int imx_pwm_apply_v2(struct pwm_chip *chip,
> struct pwm_device *pwm,
> cr |= MX3_PWMCR_POUTC;
>
> writel(cr, imx->mmio_base + MX3_PWMCR);
> - } else {
> + } else if (cstate.enabled) {
> writel(0, imx->mmio_base + MX3_PWMCR);
>
> clk_disable_unprepare(imx->clk_per);
>
>
> This would not disable a disabled PWM anymore, I guess at normal use not
> a problem. Only at bootup it could end up left on, but I guess if we
> care about boot time transition we should implement get_state, but
> something which we can do in a follow up patch.
Yep, that's a different problem which could be addressed by
implementing ->get_state(). Note that you don't necessary want to
disable the PWM at boot time, in some situation, when the PWM is
driving a critical device (like the VDDIODDR regulator), you want the
transition between the bootloader/firmware and Linux to be as smooth as
possible. Actually, 'initial state retrieval' and 'atomic changes'
were added to handle this case.
Stefan, one last thing, can you apply patch 2 alone and check if it
doesn't introduce a regression?
Thanks,
Boris
next prev parent reply other threads:[~2017-01-10 7:59 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-04 23:36 [PATCH v4 00/11] pwm: imx: Provide atomic operation for IMX PWM driver Lukasz Majewski
2017-01-04 23:36 ` [PATCH v4 01/11] pwm: print error messages with pr_err() instead of pr_debug() Lukasz Majewski
2017-01-04 23:36 ` [PATCH v4 02/11] pwm: imx: remove ipg clock and enable per clock when required Lukasz Majewski
2017-01-05 7:14 ` Boris Brezillon
2017-01-05 7:26 ` Lukasz Majewski
2017-01-05 8:27 ` Boris Brezillon
2017-01-05 8:32 ` Lukasz Majewski
2017-01-10 17:28 ` Stefan Agner
2017-01-04 23:36 ` [PATCH v4 03/11] pwm: imx: Add separate set of pwm ops for PWMv1 and PWMv2 Lukasz Majewski
2017-01-04 23:36 ` [PATCH v4 04/11] pwm: imx: Rewrite imx_pwm_*_v1 code to facilitate switch to atomic pwm operation Lukasz Majewski
2017-01-04 23:36 ` [PATCH v4 05/11] pwm: imx: Move PWMv2 software reset code to a separate function Lukasz Majewski
2017-01-04 23:36 ` [PATCH v4 06/11] pwm: imx: Move PWMv2 wait for fifo slot " Lukasz Majewski
2017-01-04 23:36 ` [PATCH v4 07/11] pwm: imx: Provide atomic PWM support for i.MX PWMv2 Lukasz Majewski
2017-01-05 8:50 ` Boris Brezillon
2017-01-05 9:03 ` Lukasz Majewski
2017-01-05 9:19 ` Boris Brezillon
2017-01-05 9:35 ` Lukasz Majewski
2017-01-05 9:53 ` Boris Brezillon
2017-01-10 3:14 ` Stefan Agner
2017-01-10 7:59 ` Boris Brezillon [this message]
2017-01-05 21:15 ` Andy Shevchenko
2017-01-06 7:06 ` Boris Brezillon
2017-01-07 18:35 ` Lukasz Majewski
2017-01-04 23:36 ` [PATCH v4 08/11] pwm: imx: Remove redundant i.MX PWMv2 code Lukasz Majewski
2017-01-04 23:36 ` [PATCH v4 09/11] pwm: core: make the PWM_POLARITY flag in DTB optional Lukasz Majewski
2017-01-04 23:36 ` [PATCH v4 10/11] pwm: imx: doc: Update imx-pwm.txt documentation entry Lukasz Majewski
2017-01-04 23:36 ` [PATCH v4 11/11] pwm: imx: Add polarity inversion support to i.MX's PWMv2 Lukasz Majewski
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170110085909.69b80820@bbrezillon \
--to=boris.brezillon@free-electrons.com \
--cc=LW@karo-electronics.de \
--cc=bhuvanchandra.dv@toradex.com \
--cc=fabio.estevam@nxp.com \
--cc=kernel@pengutronix.de \
--cc=l.majewski@majess.pl \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pwm@vger.kernel.org \
--cc=lukma@denx.de \
--cc=s.hauer@pengutronix.de \
--cc=stefan@agner.ch \
--cc=thierry.reding@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).