linux-kernel - Re: [PATCH v2 05/11] driver core: fw_devlink: Add DL_FLAG

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Message-ID: <Y9OZh0ZqtnqmKcvT@smile.fi.intel.com>
Date:   Fri, 27 Jan 2023 11:29:43 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Cristian Marussi <cristian.marussi@....com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Len Brown <lenb@...nel.org>,
        Daniel Scally <djrscally@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Tony Lindgren <tony@...mide.com>,
        Linux Kernel Functional Testing <lkft@...aro.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Abel Vesa <abel.vesa@...aro.org>,
        Alexander Stein <alexander.stein@...tq-group.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        John Stultz <jstultz@...gle.com>,
        Doug Anderson <dianders@...omium.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Maxim Kiselev <bigunclemax@...il.com>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Luca Weiss <luca.weiss@...rphone.com>,
        Colin Foster <colin.foster@...advantage.com>,
        Martin Kepplinger <martin.kepplinger@...i.sm>,
        Jean-Philippe Brucker <jpb@...nel.org>,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 05/11] driver core: fw_devlink: Add DL_FLAG_CYCLE
 support to device links

On Thu, Jan 26, 2023 at 04:11:32PM -0800, Saravana Kannan wrote:
> fw_devlink uses DL_FLAG_SYNC_STATE_ONLY device link flag for two
> purposes:
> 
> 1. To allow a parent device to proxy its child device's dependency on a
>    supplier so that the supplier doesn't get its sync_state() callback
>    before the child device/consumer can be added and probed. In this
>    usage scenario, we need to ignore cycles for ensure correctness of
>    sync_state() callbacks.
> 
> 2. When there are dependency cycles in firmware, we don't know which of
>    those dependencies are valid. So, we have to ignore them all wrt
>    probe ordering while still making sure the sync_state() callbacks
>    come correctly.
> 
> However, when detecting dependency cycles, there can be multiple
> dependency cycles between two devices that we need to detect. For
> example:
> 
> A -> B -> A and A -> C -> B -> A.
> 
> To detect multiple cycles correct, we need to be able to differentiate
> DL_FLAG_SYNC_STATE_ONLY device links used for (1) vs (2) above.
> 
> To allow this differentiation, add a DL_FLAG_CYCLE that can be use to
> mark use case (2). We can then use the DL_FLAG_CYCLE to decide which
> DL_FLAG_SYNC_STATE_ONLY device links to follow when looking for
> dependency cycles.

...

> +static inline bool device_link_flag_is_sync_state_only(u32 flags)
> +{
> +	return (flags & ~(DL_FLAG_INFERRED | DL_FLAG_CYCLE))
> +		== (DL_FLAG_SYNC_STATE_ONLY | DL_FLAG_MANAGED);

Weird indentation, why not

	return (flags & ~(DL_FLAG_INFERRED | DL_FLAG_CYCLE)) ==
	       (DL_FLAG_SYNC_STATE_ONLY | DL_FLAG_MANAGED);

?

> +}

...

>  			       DL_FLAG_AUTOREMOVE_SUPPLIER | \
>  			       DL_FLAG_AUTOPROBE_CONSUMER  | \
>  			       DL_FLAG_SYNC_STATE_ONLY | \
> -			       DL_FLAG_INFERRED)
> +			       DL_FLAG_INFERRED | \
> +			       DL_FLAG_CYCLE)

You can make less churn by squeezing the new one above the last one.

-- 
With Best Regards,
Andy Shevchenko