Re: [PATCH 1/1] regmap: cache: downgrade log level for no cache defaults message

From: Alexander Stein
Date: Mon Nov 28 2022 - 09:58:47 EST


Hello Mark,

Am Freitag, 25. November 2022, 20:30:52 CET schrieb Mark Brown:
> * PGP Signed by an unknown key
>
> On Wed, Sep 21, 2022 at 09:10:54AM +0200, Alexander Stein wrote:
> > Having no cache defaults is not a mistake, especially for devices
> > which do have some kind of strapping values which can't be provided
> > statically. For this case a warning is the wrong log level, the initial
> > cache values do need to be read form hardware. Reduce level to info.
> >
> > if (!map->reg_defaults_raw) {
> >
> > bool cache_bypass = map->cache_bypass;
> >
> > - dev_warn(map->dev, "No cache defaults, reading back from
HW\n");
> > + dev_info(map->dev, "No cache defaults, reading back from
HW\n");
>
> This is a warning which is only generated in the case where we have a
> non-sparse cache where we won't read from the hardware in the csae of
> missing values and will instead just substitute zero as a default value.
> It's warning that we might end up changing values for the device
> unexpectedly in the case of a read/modify/write cycle that doesn't
> actually check what the device currently has set.
>
> In this case if you can't use a rbtree cache I would recommend
> bootstrapping by initially reading without a cache first to get the
> default values, then replacing the regmap with one that uses the
> defaults you just read. You'll need some care over suspend/resume
> though.

The driver I'm working on clk-renesas-pcie.c only has 8 registers, so there is
no benefit to use a different cache than REGCACHE_FLAT.

But I currently fail to see why this is only for non-sparse caches. This is
printed even before the cache_ops init() is called.

Before the call to regcache_hw_init() there is this comment:
> /* Some devices such as PMICs don't have cache defaults,
> * we cope with this by reading back the HW registers and
> * crafting the cache defaults by hand.
> */

This is exactly what I want to do: Read back HW registers and create a cache.
Actually regcache_hw_init() is exactly doing what you are suggesting:
1. reading HW registers into map->reg_defaults_raw
2.
a) copy them into map->reg_defaults
b) read HW register individually if 1. failed

So thinking more about this, this warning should be removed altogether IMHO.

Best regards,
Alexander