linux-kernel - Re: [PATCH] regmap: Allocate buffers with GFP_ATOMIC when fast

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Date:	Fri, 11 Sep 2015 09:16:47 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Mark Brown <broonie@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Abhijeet Dharmapurikar <adharmap@...eaurora.org>
Subject: Re: [PATCH] regmap: Allocate buffers with GFP_ATOMIC when fast_io ==
 true

On 09/11, Mark Brown wrote:
> On Thu, Sep 10, 2015 at 12:27:01PM -0700, Stephen Boyd wrote:
> > If a regmap is using fast_io, allocate buffers in the write APIs
> > with GFP_ATOMIC instead of GFP_KERNEL. Otherwise we may schedule
> > while atomic.
> 
> Why is this needed?  If something needs fast I/O it probably doesn't
> want to be going down any of the code paths that result in us doing
> allocations.  I'd expect either no cache, a flat cache or setting up
> defaults at initialisation time.

We tripped over this with regmap_bulk_write() users on the SPMI
bus. How about going down the same paths as !map->can_multi_write
and map->use_single_rw if fast_io == true? Something like this
untested patch.

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 29128c6af445..4f2d75527c7f 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -573,8 +573,8 @@ struct regmap *regmap_init(struct device *dev,
 		map->reg_stride = config->reg_stride;
 	else
 		map->reg_stride = 1;
-	map->use_single_rw = config->use_single_rw;
-	map->can_multi_write = config->can_multi_write;
+	map->use_single_rw = config->use_single_rw || config->fast_io;
+	map->can_multi_write = config->can_multi_write && !config->fast_io;
 	map->dev = dev;
 	map->bus = bus;
 	map->bus_context = bus_context;

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