Re: [PATCH v15 12/12] of: Add plumbing for restricted DMA pool

[Guenter Roeck <linux@xxxxxxxxxxxx>]

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@xxxxxxxxxxxx>
> > > > Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > > > Tested-by: Will Deacon <will@xxxxxxxxxx>
> > > 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@xxxxxxxxxx>
> 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@xxxxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> Suggested-by: Robin Murphy <robin.murphy@xxxxxxx>
> Link: https://lore.kernel.org/r/20210702030807.GA2685166@xxxxxxxxxxxx
> Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>

> ---
>   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
>