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Message-ID: <0cb645c7-f3c5-e4bb-7686-2a83d32274bb@axentia.se>
Date: Fri, 20 Oct 2023 16:28:12 +0200
From: Peter Rosin <peda@...ntia.se>
To: Andrew Davis <afd@...com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Rob Herring <robh+dt@...nel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Nishanth Menon <nm@...com>,
Vignesh Raghavendra <vigneshr@...com>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mux: mmio: use reg property when parent device is not
a syscon
Hi!
2023-09-11 at 17:10, Andrew Davis wrote:
> The DT binding for the reg-mux compatible states it can be used when the
> "parent device of mux controller is not syscon device". It also allows
> for a reg property. When the reg property is provided, use that to
> identify the address space for this mux. If not provided fallback to
> using the parent device as a regmap provider.
>
> Signed-off-by: Andrew Davis <afd@...com>
> Reviewed-by: Nishanth Menon <nm@...com>
> ---
>
> Changes from v2:
> - Rebased on v6.6-rc1
>
> Changes from v1:
> - Flip logic as suggested in v1[0]
>
> [0] https://lore.kernel.org/lkml/1c27d9d4-b1cc-c158-90f7-f7e47e02c424@ti.com/T/
>
> drivers/mux/mmio.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mux/mmio.c b/drivers/mux/mmio.c
> index fd1d121a584ba..b6095b7853ed2 100644
> --- a/drivers/mux/mmio.c
> +++ b/drivers/mux/mmio.c
> @@ -44,10 +44,13 @@ static int mux_mmio_probe(struct platform_device *pdev)
> int ret;
> int i;
>
> - if (of_device_is_compatible(np, "mmio-mux"))
> + if (of_device_is_compatible(np, "mmio-mux")) {
> regmap = syscon_node_to_regmap(np->parent);
> - else
> - regmap = dev_get_regmap(dev->parent, NULL) ?: ERR_PTR(-ENODEV);
> + } else {
> + regmap = device_node_to_regmap(np);
I started digging in device_node_to_regmap() to try to find an error that
could be used to trigger if the failover to dev_get_regmap() should be
tried, instead of always doing the failover on error. I got lost fairly
quickly, but it seems device_node_to_regmap() can return -EDEFER_PROBE.
While I'm not certain that it is applicable, that case should probably
not fall back to dev_get_regmap()...
Are there other error cases that should prevent the failover? I would
guess that it's perhaps just a single error that should trigger trying
the failover path? But I don't know, and which error if that's the case?
How much badness can be caused if syscon_node_to_regmap() fails for some
random obscure reason and the failover path is taken inadvertently? It
certainly smells bad for -EDEFER_PROBE, but do you have any insight in
other cases?
And after getting to approx that point a while back, I had other things
to take care of, and this fell off the table. Sorry!
Cheers,
Peter
> + if (IS_ERR(regmap))
> + regmap = dev_get_regmap(dev->parent, NULL) ?: ERR_PTR(-ENODEV);
> + }
> if (IS_ERR(regmap)) {
> ret = PTR_ERR(regmap);
> dev_err(dev, "failed to get regmap: %d\n", ret);
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