linux-kernel - Re: [PATCH 2/2] [media] exynos-gsc: Fix imprecise external abort due disabled power domain

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Message-id: <cc9c6837-7141-b63c-ddf6-68252493df11@samsung.com>
Date:   Thu, 19 Jan 2017 15:17:13 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Javier Martinez Canillas <javier@....samsung.com>,
        linux-kernel@...r.kernel.org
Cc:     Inki Dae <inki.dae@...sung.com>,
        Andi Shyti <andi.shyti@...sung.com>,
        Shuah Khan <shuahkh@....samsung.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Kukjin Kim <kgene@...nel.org>,
        linux-samsung-soc@...r.kernel.org,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        linux-media@...r.kernel.org, Krzysztof Kozlowski <krzk@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH 2/2] [media] exynos-gsc: Fix imprecise external abort due
 disabled power domain

Hi Javier,

On 2017-01-18 01:30, Javier Martinez Canillas wrote:
> Commit 15f90ab57acc ("[media] exynos-gsc: Make driver functional when
> CONFIG_PM is unset") removed the implicit dependency that the driver
> had with CONFIG_PM, since it relied on the config option to be enabled.
>
> In order to work with !CONFIG_PM, the GSC reset logic that happens in
> the runtime resume callback had to be executed on the probe function.
>
> The problem is that if CONFIG_PM is enabled, the power domain for the
> GSC could be disabled and so an attempt to write to the GSC_SW_RESET
> register leads to an unhandled fault / imprecise external abort error:

Driver core ensures that driver's probe() is called with respective power
domain turned on, so this is not the right reason for the proposed change.

> [   10.178825] Unhandled fault: imprecise external abort (0x1406) at 0x00000000
> [   10.186982] pgd = ed728000
> [   10.190847] [00000000] *pgd=00000000
> [   10.195553] Internal error: : 1406 [#1] PREEMPT SMP ARM
> [   10.229761] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
> [   10.237134] task: ed49e400 task.stack: ed724000
> [   10.242934] PC is at gsc_wait_reset+0x5c/0x6c [exynos_gsc]
> [   10.249710] LR is at gsc_probe+0x300/0x33c [exynos_gsc]
> [   10.256139] pc : [<bf2429e0>]    lr : [<bf240734>]    psr: 60070013
> [   10.256139] sp : ed725d30  ip : 00000000  fp : 00000001
> [   10.271492] r10: eea74800  r9 : ecd6a2c0  r8 : ed7d8854
> [   10.277912] r7 : ed7d8c08  r6 : ed7d8810  r5 : ffff8ecd  r4 : c0c03900
> [   10.285664] r3 : 00000000  r2 : 00000001  r1 : ed7d8b98  r0 : ed7d8810
>
> So only do a GSC reset if CONFIG_PM is disabled, since if is enabled the
> runtime PM resume callback will be called by the VIDIOC_STREAMON ioctl,
> making the reset in probe unneeded.
>
> Fixes: 15f90ab57acc ("[media] exynos-gsc: Make driver functional when CONFIG_PM is unset")
> Signed-off-by: Javier Martinez Canillas <javier@....samsung.com>

Frankly, I don't get why this change is needed.

>
> ---
>
> I-ve only tested with CONFIG_PM enabled since my Exynos5422 Odroid
> XU4 board fails to boot when the config option is disabled.
>
> Best regards,
> Javier
>
>   drivers/media/platform/exynos-gsc/gsc-core.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/platform/exynos-gsc/gsc-core.c b/drivers/media/platform/exynos-gsc/gsc-core.c
> index 83272f10722d..42e1e09ea915 100644
> --- a/drivers/media/platform/exynos-gsc/gsc-core.c
> +++ b/drivers/media/platform/exynos-gsc/gsc-core.c
> @@ -1083,8 +1083,10 @@ static int gsc_probe(struct platform_device *pdev)
>   
>   	platform_set_drvdata(pdev, gsc);
>   
> -	gsc_hw_set_sw_reset(gsc);
> -	gsc_wait_reset(gsc);
> +	if (!IS_ENABLED(CONFIG_PM)) {
> +		gsc_hw_set_sw_reset(gsc);
> +		gsc_wait_reset(gsc);
> +	}
>   
>   	vb2_dma_contig_set_max_seg_size(dev, DMA_BIT_MASK(32));
>   

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland