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@xxxxxx>
Reviewed-by: Nishanth Menon <nm@xxxxxx>
---
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@xxxxxx/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);
