Messages in this thread | | | Date | Mon, 23 Oct 2023 11:26:09 -0500 | Subject | Re: [PATCH v3] mux: mmio: use reg property when parent device is not a syscon | From | Andrew Davis <> |
| |
On 10/20/23 4:22 PM, Peter Rosin wrote: > Hi! > > 2023-10-20 at 18:43, Andrew Davis wrote: >> 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. > > The ideal working case is usually not much of a problem. When I look at what > device_node_to_regmap does, I find, appart from -ENOMEM, possibilities of > -ENOENT (because no clock), and the clock may theoretically fail to prepare > for numerous reasons hidden in clock drivers, but the clock core can > trigger at least -EACCES and -EINPROGRESS via runtime PM. > > And it definitely looks like the -EPROBE_DEFER case needs to be addressed. > I.e., why is this call chain not a problem? > > mux_mmio_probe > ->device_node_to_regmap > -> device_node_get_regmap > -> of_syscon_register > -> of_hwspin_lock_get_id > <- -EPROBE_DEFER > <- ERR_PTR(-EPROBE_DEFER) > <- ERR_PTR(-EPROBE_DEFER) > <- ERR_PTR(-EPROBE_DEFER) > > As far as I can tell, if device_node_to_regmap() fails with -EPROBE_DEFER > with your patch, then mux_mmio_probe() misbehaves. It should have aborted > and failed with -EPROBE_DEFER, but instead throws that error away and > goes on to try dev_get_regmap(). That, in turn, is probably futile and > will likely error out in some way, breaking a system that might have been > ok, if the probe had been retried some time later. >
This is why I liked the v1 version, dev_get_regmap() just returns a simple NULL on error, no complex EPROBE_DEFER oddness :)
So is EPROBE_DEFER the only one we think should retry and not go down the fallback path? I believe that is the normal assumption for most drivers.
> As long as the above is not sufficiently explained away, or fixed, I > consider the patch broken. > >>> 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). > > Hold your horses, I need the above explanation first (and perhaps an > updated patch). >
I'm not normally so impatient but this went two whole kernel cycles without any comment until rc6.. v4 on the way.
Andrew
> Cheers, > Peter > >> 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);
| |