linux-kernel - Re: [PATCH RFC v3 1/8] of: Mark interconnects property supplier as optional

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Date:   Mon, 7 Mar 2022 17:21:34 -0600
From:   Rob Herring <robh@...nel.org>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Saravana Kannan <saravanak@...gle.com>
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Maxime Ripard <mripard@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH RFC v3 1/8] of: Mark interconnects property supplier as
 optional

+Saravana

On Wed, Mar 02, 2022 at 10:10:53PM +0100, Paul Kocialkowski wrote:
> In order to set their correct DMA address offset, some devices rely on
> the device-tree interconnects property which identifies an
> interconnect node that provides a dma-ranges property that can be used
> to set said offset.
> 
> Since that logic is all handled by the generic openfirmware and driver
> code, the device-tree description could be enough to properly set
> the offset.
> 
> However the interconnects property is currently not marked as
> optional, which implies that a driver for the corresponding node
> must be loaded as a requirement. When no such driver exists, this
> results in an endless EPROBE_DEFER which gets propagated to the
> calling driver. This ends up in the driver never loading.
> 
> Marking the interconnects property as optional makes it possible
> to load the driver in that situation, since the EPROBE_DEFER return
> code will no longer be propagated to the driver.
> 
> There might however be undesirable consequences with this change,
> which I do not fully grasp at this point.
> 
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> ---
>  drivers/of/property.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index 8e90071de6ed..ef7c56b510e8 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -1365,7 +1365,7 @@ static struct device_node *parse_interrupts(struct device_node *np,
>  
>  static const struct supplier_bindings of_supplier_bindings[] = {
>  	{ .parse_prop = parse_clocks, },
> -	{ .parse_prop = parse_interconnects, },
> +	{ .parse_prop = parse_interconnects, .optional = true,},
>  	{ .parse_prop = parse_iommus, .optional = true, },
>  	{ .parse_prop = parse_iommu_maps, .optional = true, },
>  	{ .parse_prop = parse_mboxes, },
> -- 
> 2.35.1
> 
>