mmc: Aggressive clock gating framework

This patch modifies the MMC core code to optionally call the set_ios()
operation on the driver with the clock frequency set to 0 (gate) after
a grace period of at least 8 MCLK cycles, then restore it (ungate)
before any new request. This gives the driver the option to shut down
the MCI clock to the MMC/SD card when the clock frequency is 0, i.e.
the core has stated that the MCI clock does not need to be generated.

It is inspired by existing clock gating code found in the OMAP and
Atmel drivers and brings this up to the host abstraction.  Gating is
performed before and after any MMC request.

This patchset implements this for the MMCI/PL180 MMC/SD host controller,
but it should be simple to switch OMAP/Atmel over to using this instead.

mmc_set_{gated,ungated}() add variable protection to the state holders
for the clock gating code.  This is particularly important when ordinary
.set_ios() calls would race with the .set_ios() call resulting from a
delayed gate operation.

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Reviewed-by: Chris Ball <cjb@laptop.org>
Tested-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 30f6fad99a58..381c77fd4dca 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -172,6 +172,16 @@ struct mmc_host {
 
         mmc_pm_flag_t           pm_caps;        /* supported pm features */
 
+#ifdef CONFIG_MMC_CLKGATE
+        int                     clk_requests;   /* internal reference counter */
+        unsigned int            clk_delay;      /* number of MCI clk hold cycles */
+        bool                    clk_gated;      /* clock gated */
+        struct work_struct      clk_gate_work; /* delayed clock gate */
+        unsigned int            clk_old;        /* old clock value cache */
+        spinlock_t              clk_lock;       /* lock for clk fields */
+        struct mutex            clk_gate_mutex; /* mutex for clock gating */
+#endif
+
         /* host specific block data */
         unsigned int            max_seg_size;   /* see blk_queue_max_segment_size */
         unsigned short          max_segs;       /* see blk_queue_max_segments */