From mboxrd@z Thu Jan  1 00:00:00 1970
From: Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH v8 07/14] ARM: dts: rockchip: add clocks in iommu nodes
Date: Mon, 9 Apr 2018 16:53:01 +0100
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To: =?UTF-8?Q?Heiko_St=c3=bcbner?= <heiko@sntech.de>, Tomeu Vizoso <tomeu@tomeuvizoso.net>
Cc: Jeffy Chen <jeffy.chen@rock-chips.com>, open list <linux-kernel@vger.kernel.org>, jcliang@chromium.org, simon xue <xxm@rock-chips.com>, tfiga@chromium.org, Romain Perier <romain.perier@collabora.com>, Yakir Yang <kuankuan.y@gmail.com>, Arnd Bergmann <arnd@arndb.de>, Liang Chen <cl@rock-chips.com>, Rob Herring <robh+dt@kernel.org>, Shawn Lin <shawn.lin@rock-chips.com>, Catalin Marinas <catalin.marinas@arm.com>, David Wu <david.wu@rock-chips.com>, Finley Xiao <finley.xiao@rock-chips.com>, Enric Balletbo i Serra <enric.balletbo@collabora.com>, Jacob Chen <jacob-chen@iotwrt.com>, Kever Yang <kever.yang@rock-chips.com>, Brian Norris <briannorris@chromium.org>, "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>, Rocky Hao <rocky.hao@rock-chips.co>
List-Id: devicetree@vger.kernel.org

On 09/04/18 16:44, Heiko Stübner wrote:
> Hi Tomeu,
> 
> Am Montag, 9. April 2018, 16:41:56 CEST schrieb Tomeu Vizoso:
>> in today's linux-next, the DRM driver fails to probe because the iommu
>> driver fails to find the aclk. I need to apply this patch for things
>> to work again.
> 
> Thanks for catching that issue.
> 
> This seems to expose a backwards-compatibility issue, as this breaks
> all old devicetrees, so should get a proper fix, apart from me applying
> the dt-patch I missed.
> 
> Looking at the iommu-clock-handling patch, I imagine this part as
> the culprit:
> 
> +	iommu->num_clocks = ARRAY_SIZE(rk_iommu_clocks);
> +	iommu->clocks = devm_kcalloc(iommu->dev, iommu->num_clocks,
> +				     sizeof(*iommu->clocks), GFP_KERNEL);
> +	if (!iommu->clocks)
> +		return -ENOMEM;
> 
> The clk-bulk functions seem to work with simple for loops and
> should (as the other standard clock functions) just work fine with
> an empty struct, so I guess a simple
> 
> 	if (!iommu->clocks && iommu->num_clocks > 0)
> 		return -ENOMEM;
> 
> should hopefully be enough. I'll try to give this a test later on
> if nobody beats me to it :-)

But iommu->num_clocks is clearly set to a nonzero compile-time constant 
at this point ;)

I'd assume it's the return from devm_clk_bulk_get() which needs to 
special-case the "no clocks found" case from any other error, and *then* 
blat num_clocks to 0 if so.

Robin.