Re: [RFC PATCH 2/2] regmap: Reject fast_io regmap configurations with RBTREE and MAPLE caches

[Guenter Roeck]

On 7/21/23 07:53, Marek Szyprowski wrote:
> Hi,
>
> On 20.07.2023 05:28, Guenter Roeck wrote:
> > REGCACHE_RBTREE and REGCACHE_MAPLE dynamically allocate memory for regmap
> > operations. This is incompatible with spinlock based locking which is used
> > for fast_io operations. Reject affected configurations.
> >
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> > This seems prudent, given that accesses will be protected by spinlock
> > but may allocate memory with GFP_KERNEL. Another option might be to use
> > WARN_ON instead of rejecting the configuration to avoid hard regressions
> > (and I think both drivers/net/ieee802154/mcr20a.c and
> > sound/soc/codecs/sti-sas.c may be affected, though I can not test it).
>
> This patch, which landed in today's linux-next, breaks operation of the
> RockChip's VOP2 DRM driver
> (drivers/gpu/drm/rockchip/rockchip_drm_vop2.c). I'm not sure what is the
> proper fix in this case. Should one change the cache type to REGCACHE_FLAT?

Ah, I missed regcache_init_mmio() when looking for affected drivers.
This affects a larger number of drivers than I thought. In addition
to the drivers mentioned above,

 drivers/soc/qcom/icc-bwmon.c
 sound/soc/bcm/bcm2835-i2s.c
 sound/soc/codecs/jz4740.c
 sound/soc/fsl/fsl_aud2htx.c
 sound/soc/fsl/fsl_easrc.c
 sound/soc/fsl/fsl_micfil.c

all use unsafe locking (spinlock with REGCACHE_RBTREE).

Thanks,
Guenter

> >    drivers/base/regmap/regmap.c | 9 +++++++++
> >    1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
> > index 89a7f1c459c1..b4640285c0b9 100644
> > --- a/drivers/base/regmap/regmap.c
> > +++ b/drivers/base/regmap/regmap.c
> > @@ -777,6 +777,15 @@ struct regmap *__regmap_init(struct device *dev,
> >    	} else {
> >    		if ((bus && bus->fast_io) ||
> >    		    config->fast_io) {
> > +			/*
> > +			 * fast_io is incompatible with REGCACHE_RBTREE and REGCACHE_MAPLE
> > +			 * since both need to dynamically allocate memory.
> > +			 */
> > +			if (config->cache_type == REGCACHE_RBTREE ||
> > +			    config->cache_type == REGCACHE_MAPLE) {
> > +				ret = -EINVAL;
> > +				goto err_name;
> > +			}
> >    			if (config->use_raw_spinlock) {
> >    				raw_spin_lock_init(&map->raw_spinlock);
> >    				map->lock = regmap_lock_raw_spinlock;
>
> Best regards