linux-kernel - Re: [RFC PATCH v4 7/8] pwm: Add dummy pwmchip for orphan pwms

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Date:   Wed, 18 Oct 2017 13:16:16 +0800
From:   jeffy <jeffy.chen@...k-chips.com>
To:     Mark Brown <broonie@...nel.org>,
        Brian Norris <briannorris@...omium.org>
CC:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Heiko Stübner <heiko@...ech.de>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Doug Anderson <dianders@...omium.org>, tfiga@...omium.org,
        seanpaul@...omium.org,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>
Subject: Re: [RFC PATCH v4 7/8] pwm: Add dummy pwmchip for orphan pwms

Hi guys,

On 10/18/2017 03:05 AM, Mark Brown wrote:
> On Tue, Oct 17, 2017 at 11:53:01AM -0700, Brian Norris wrote:
>> On Tue, Oct 17, 2017 at 07:46:03PM +0100, Mark Brown wrote:
>
>>> I would expect we can get a long way in the DT by doing a pass over the
>>> tree and adding links between device nodes in cases where phandle
>>> references exist.  There is a potential issue with circular links which
>>> I'm just going to handwave away right now but I'd expect that to help
>>> otherwise.
>
>> But I didn't think FDTs encoded type info. So you don't really know
>> whether a phandle is a phandle -- it's just an int (which happens to
>> have a corresponding property in some other node). Are we trusting our
>> DT bindings well enough to say that, for example, we know that in any
>> given device node, a property like 'pwms' must be a phandle to a PWM
>> provider? OK, maybe 'pwms' is a bad example (it's unlikely to get
>> reused, and it has a companion '#pwm-cells' property), but grepping the
>> DT bindings directory shows a ton of one-off properties that contain
>> phandles.
>
> If we're going with the 90% thing we can probably get a long way with a
> whitelist of properties, and we'll be able to take that a lot further
> with the validatable schemas if they ever happen.
>

so it looks like we are going to use device link in common code to fix 
this issue(and also other dependency issue), then i will drop this patch 
and the followed rockchip drm device link patch in next version :)


also the reason why i try to use dummy chip instead is that:

currently we have these devices: rockchip spi device(master) -> 
cros_ec_spi device(child) -> cros_ec_pwm(spi based pwm) -> pwm_bl

i added device link to cros_ec_pwm and pwm_bl, that works well for 
unbind/bind cros_ec_pwm device case, but there's a warning when i try to 
unbind cros_ec_spi:


static void device_links_purge(struct device *dev)
{
...
         list_for_each_entry_safe_reverse(link, ln, 
&dev->links.consumers, s_node) {
                 WARN_ON(link->status != DL_STATE_DORMANT &&
                         link->status != DL_STATE_NONE);        <--- hit 
warning here!
                 __device_link_del(link);
         }


but i checked again, that could due to the way spi core unregester 
children devices. maybe it need to call device_release_driver