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From: Evan Green <evgreen@chromium.org>
To: Yong Wu <yong.wu@mediatek.com>
Cc: Joerg Roedel <joro@8bytes.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Rob Herring <robh+dt@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Tomasz Figa <tfiga@google.com>, Will Deacon <will.deacon@arm.com>,
	linux-mediatek@lists.infradead.org, srv_heupstream@mediatek.com,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	iommu@lists.linux-foundation.org, Arnd Bergmann <arnd@arndb.de>,
	yingjoe.chen@mediatek.com, youlin.pei@mediatek.com,
	Nicolas Boichat <drinkcat@chromium.org>
Subject: Re: [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag
Date: Mon, 25 Feb 2019 15:53:44 -0800	[thread overview]
Message-ID: <CAE=gft7mWs1jc+KQQcPuuhcmxpFRnRBTt35+uC3F20N6R554bQ@mail.gmail.com> (raw)
In-Reply-To: <1546318276-18993-3-git-send-email-yong.wu@mediatek.com>

On Mon, Dec 31, 2018 at 8:52 PM Yong Wu <yong.wu@mediatek.com> wrote:
>
> DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link
> automatically on consumer/supplier driver unbind", that means we should
> remove whole the device_link when there is no this driver no matter what
> the ref_count of the link is.
>
> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Yong Wu <yong.wu@mediatek.com>
> ---
> The ref_count of our device_link normally is over 1. When the consumer
> device driver is removed, whole the device_link should be removed.
> Thus, I add this patch.
> ---

I will admit to reading about device links for the first time while
reviewing this patch, but I don't really get this. Why use a kref at
all if we're just going to ignore its value? For instance, I see that
if you call device_link_add() with the same supplier and consumer, it
uses the kref to return the same link. That machinery is broken with
your change. Although I don't see any uses of it, you might also
expect a supplier or consumer could do a kref_get() on the link it got
back from device_link_add(), and have a reasonable expectation that
the link wouldn't be freed out from under it. This would also be
broken.

Can you explain why your device_links normally have a reference count
>1, and why those additional references can't be cleaned up in an
orderly fashion?

(To be honest, I don't really understand the case for the AUTOREMOVE
flags at all. Is there some case where the party that set up the link
can't tear it down? Or is this a way to devm_ify the link, where devm
itself doesn't work because the links themselves stall out that
mechanism?)

  reply	other threads:[~2019-02-26  0:02 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-01  4:51 [PATCH 00/13] Clean up "mediatek,larb" after adding device_link Yong Wu
2019-01-01  4:51 ` [PATCH 01/13] dt-binding: mediatek: Get rid of mediatek,larb for multimedia HW Yong Wu
2019-01-11 14:58   ` Rob Herring
2019-02-25 23:54   ` Evan Green
2019-01-01  4:51 ` [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag Yong Wu
2019-02-25 23:53   ` Evan Green [this message]
2019-02-27 14:33     ` Yong Wu
2019-03-05 19:03       ` Evan Green
2019-03-12 14:21         ` Matthias Brugger
2019-03-12 23:17           ` Evan Green
2019-03-13  9:08             ` Yong Wu
2019-01-01  4:51 ` [PATCH 03/13] iommu/mediatek: Add probe_defer for smi-larb Yong Wu
2019-02-25 23:54   ` Evan Green
2019-02-27 14:33     ` Yong Wu
2019-03-05 19:02       ` Evan Green
2019-01-01  4:51 ` [PATCH 04/13] iommu/mediatek: Add device_link between the consumer and the larb devices Yong Wu
2019-02-25 23:54   ` Evan Green
2019-02-27 14:34     ` Yong Wu
2019-02-27 19:30   ` Robin Murphy
2019-03-13  9:11     ` Yong Wu
2019-01-01  4:51 ` [PATCH 05/13] memory: mtk-smi: Add device-link between smi-larb and smi-common Yong Wu
2019-02-25 23:54   ` Evan Green
2019-02-27 14:33     ` Yong Wu
2019-03-05 19:02       ` Evan Green
2019-01-01  4:51 ` [PATCH 06/13] media: mtk-jpeg: Get rid of mtk_smi_larb_get/put Yong Wu
2019-02-25 23:55   ` Evan Green
2019-01-01  4:51 ` [PATCH 07/13] media: mtk-mdp: " Yong Wu
2019-02-25 23:55   ` Evan Green
2019-01-01  4:51 ` [PATCH 08/13] media: mtk-vcodec: " Yong Wu
2019-02-25 23:55   ` Evan Green
2019-01-01  4:51 ` [PATCH 09/13] drm/mediatek: " Yong Wu
2019-02-25 23:55   ` Evan Green
2019-01-01  4:51 ` [PATCH 10/13] memory: mtk-smi: " Yong Wu
2019-02-25 23:56   ` Evan Green
2019-01-01  4:51 ` [PATCH 11/13] iommu/mediatek: Use builtin_platform_driver Yong Wu
2019-02-25 23:56   ` Evan Green
2019-02-27 14:33     ` Yong Wu
2019-03-05 19:03       ` Evan Green
2019-01-01  4:51 ` [PATCH 12/13] arm: dts: mediatek: Get rid of mediatek,larb for MM nodes Yong Wu
2019-02-25 23:56   ` Evan Green
2019-01-01  4:51 ` [PATCH 13/13] arm64: " Yong Wu
2019-02-25 23:56   ` Evan Green

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