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Sender: Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH v15 12/12] of: Add plumbing for restricted DMA pool
To:     Will Deacon <will@kernel.org>, Robin Murphy <robin.murphy@arm.com>
Cc:     Claire Chang <tientzu@chromium.org>,
        Rob Herring <robh+dt@kernel.org>, mpe@ellerman.id.au,
        Joerg Roedel <joro@8bytes.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
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        Marek Szyprowski <m.szyprowski@samsung.com>,
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References: <20210624155526.2775863-1-tientzu@chromium.org>
 <20210624155526.2775863-13-tientzu@chromium.org>
 <20210702030807.GA2685166@roeck-us.net>
 <87ca3ada-22ed-f40c-0089-ca6fffc04f24@arm.com>
 <20210702131829.GA11132@willie-the-truck>
From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <2f2d6633-2457-f7eb-81c1-355f56dc34ce@roeck-us.net>
Date:   Fri, 2 Jul 2021 06:48:54 -0700
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On 7/2/21 6:18 AM, Will Deacon wrote:
> On Fri, Jul 02, 2021 at 12:39:41PM +0100, Robin Murphy wrote:
>> On 2021-07-02 04:08, Guenter Roeck wrote:
>>> On Thu, Jun 24, 2021 at 11:55:26PM +0800, Claire Chang wrote:
>>>> If a device is not behind an IOMMU, we look up the device node and set
>>>> up the restricted DMA when the restricted-dma-pool is presented.
>>>>
>>>> Signed-off-by: Claire Chang <tientzu@chromium.org>
>>>> Tested-by: Stefano Stabellini <sstabellini@kernel.org>
>>>> Tested-by: Will Deacon <will@kernel.org>
>>>
>>> With this patch in place, all sparc and sparc64 qemu emulations
>>> fail to boot. Symptom is that the root file system is not found.
>>> Reverting this patch fixes the problem. Bisect log is attached.
>>
>> Ah, OF_ADDRESS depends on !SPARC, so of_dma_configure_id() is presumably
>> returning an unexpected -ENODEV from the of_dma_set_restricted_buffer()
>> stub. That should probably be returning 0 instead, since either way it's not
>> an error condition for it to simply do nothing.
> 
> Something like below?
> 

Yes, that does the trick.

> Will
> 
> --->8
> 
>>From 4d9dcb9210c1f37435b6088284e04b6b36ee8c4d Mon Sep 17 00:00:00 2001
> From: Will Deacon <will@kernel.org>
> Date: Fri, 2 Jul 2021 14:13:28 +0100
> Subject: [PATCH] of: Return success from of_dma_set_restricted_buffer() when
>   !OF_ADDRESS
> 
> When CONFIG_OF_ADDRESS=n, of_dma_set_restricted_buffer() returns -ENODEV
> and breaks the boot for sparc[64] machines. Return 0 instead, since the
> function is essentially a glorified NOP in this configuration.
> 
> Cc: Claire Chang <tientzu@chromium.org>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Suggested-by: Robin Murphy <robin.murphy@arm.com>
> Link: https://lore.kernel.org/r/20210702030807.GA2685166@roeck-us.net
> Signed-off-by: Will Deacon <will@kernel.org>

Tested-by: Guenter Roeck <linux@roeck-us.net>

> ---
>   drivers/of/of_private.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
> index 8fde97565d11..34dd548c5eac 100644
> --- a/drivers/of/of_private.h
> +++ b/drivers/of/of_private.h
> @@ -173,7 +173,8 @@ static inline int of_dma_get_range(struct device_node *np,
>   static inline int of_dma_set_restricted_buffer(struct device *dev,
>   					       struct device_node *np)
>   {
> -	return -ENODEV;
> +	/* Do nothing, successfully. */
> +	return 0;
>   }
>   #endif
>   
>