Messages in this thread | | | Date | Fri, 20 Oct 2023 11:43:04 -0500 | Subject | Re: [PATCH v3] mux: mmio: use reg property when parent device is not a syscon | From | Andrew Davis <> |
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On 10/20/23 9:28 AM, Peter Rosin wrote: > 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@ti.com> >> Reviewed-by: Nishanth Menon <nm@ti.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? >
Ideally the only error that will be returned is ENOMEM, which happens when this node does not have a 'reg' property, and this is also the one case we want to do the failover. So all should be well.
> 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? >
If we take the failover inadvertently then we will check if the parent node is a syscon, if it is then our offset will most likely be wrong (parent will not match child 'reg').
> 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! >
No problem as long as we can find a way to get this in quickly (lot of DT warning need cleaned up based on this patch).
Thanks Andrew
> 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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