linux-kernel - [PATCH v7 2/3] mmc: dw_mmc: Honor requests to set the clock to 0 (turn off clock)

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Message-Id: <1377794350-12335-3-git-send-email-dianders@chromium.org>
Date:	Thu, 29 Aug 2013 09:39:09 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Chris Ball <cjb@...top.org>
Cc:	Jaehoon Chung <jh80.chung@...sung.com>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	James Hogan <james.hogan@...tec.com>,
	Grant Grundler <grundler@...omium.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Abhilash Kesavan <a.kesavan@...sung.com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Olof Johansson <olof@...om.net>,
	Doug Anderson <dianders@...omium.org>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v7 2/3] mmc: dw_mmc: Honor requests to set the clock to 0 (turn off clock)

Previously the dw_mmc driver would ignore any requests to disable the
card's clock.  This doesn't seem like a good thing in general, but had
one extra bad side effect in the following situtation:
* mmc core would set clk to 400kHz at boot time while initting
* mmc core would set clk to 0 since no card, but it would be ignored.
* suspend to ram and resume; clocks in the dw_mmc IP block are now 0
  but dw_mmc thinks that they're 400kHz (it ignored the set to 0).
* insert card
* mmc core would set clk to 400kHz which would be considered a no-op.

Note that if there is no card in the slot and we do a suspend/resume
cycle, we _do_ still end up with differences in a dw_mmc register
dump, but the differences are clock related and we've got the clock
disabled both before and after, so this should be OK.

Signed-off-by: Doug Anderson <dianders@...omium.org>
---
Changes in v7:
- Avoid printing the same clock over and over again w/ MMC_CLKGATE.

Changes in v6:
- Replaces previous pathes that ensured saving/restoring clocks.

 drivers/mmc/host/dw_mmc.c | 36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index ee5f167..1584705 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -88,6 +88,8 @@ struct idmac_desc {
  * @queue_node: List node for placing this node in the @queue list of
  *	&struct dw_mci.
  * @clock: Clock rate configured by set_ios(). Protected by host->lock.
+ * @last_printed_clock: The last clock we printed.  Keeping track of this helps
+ *	us to avoid spamming the console with CONFIG_MMC_CLKGATE.
  * @flags: Random state bits associated with the slot.
  * @id: Number of this slot.
  * @last_detect_state: Most recently observed card detect state.
@@ -105,6 +107,7 @@ struct dw_mci_slot {
 	struct list_head	queue_node;
 
 	unsigned int		clock;
+	unsigned int		last_printed_clock;
 	unsigned long		flags;
 #define DW_MMC_CARD_PRESENT	0
 #define DW_MMC_CARD_NEED_INIT	1
@@ -635,7 +638,11 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
 	u32 div;
 	u32 clk_en_a;
 
-	if (slot->clock != host->current_speed || force_clkinit) {
+	if (slot->clock == 0) {
+		mci_writel(host, CLKENA, 0);
+		mci_send_cmd(slot,
+			     SDMMC_CMD_UPD_CLK | SDMMC_CMD_PRV_DAT_WAIT, 0);
+	} else if (slot->clock != host->current_speed || force_clkinit) {
 		div = host->bus_hz / slot->clock;
 		if (host->bus_hz % slot->clock && host->bus_hz > slot->clock)
 			/*
@@ -646,10 +653,14 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
 
 		div = (host->bus_hz != slot->clock) ? DIV_ROUND_UP(div, 2) : 0;
 
-		dev_info(&slot->mmc->class_dev,
-			 "Bus speed (slot %d) = %dHz (slot req %dHz, actual %dHZ"
-			 " div = %d)\n", slot->id, host->bus_hz, slot->clock,
-			 div ? ((host->bus_hz / div) >> 1) : host->bus_hz, div);
+		if (slot->clock != slot->last_printed_clock || force_clkinit) {
+			dev_info(&slot->mmc->class_dev,
+				 "Bus speed (slot %d) = %dHz (slot req %dHz, actual %dHZ div = %d)\n",
+				 slot->id, host->bus_hz, slot->clock,
+				 div ? ((host->bus_hz / div) >> 1) :
+				 host->bus_hz, div);
+			slot->last_printed_clock = slot->clock;
+		}
 
 		/* disable clock */
 		mci_writel(host, CLKENA, 0);
@@ -675,9 +686,8 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
 		/* inform CIU */
 		mci_send_cmd(slot,
 			     SDMMC_CMD_UPD_CLK | SDMMC_CMD_PRV_DAT_WAIT, 0);
-
-		host->current_speed = slot->clock;
 	}
+	host->current_speed = slot->clock;
 
 	/* Set the current slot bus width */
 	mci_writel(host, CTYPE, (slot->ctype << slot->id));
@@ -807,13 +817,11 @@ static void dw_mci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 
 	mci_writel(slot->host, UHS_REG, regs);
 
-	if (ios->clock) {
-		/*
-		 * Use mirror of ios->clock to prevent race with mmc
-		 * core ios update when finding the minimum.
-		 */
-		slot->clock = ios->clock;
-	}
+	/*
+	 * Use mirror of ios->clock to prevent race with mmc
+	 * core ios update when finding the minimum.
+	 */
+	slot->clock = ios->clock;
 
 	if (drv_data && drv_data->set_ios)
 		drv_data->set_ios(slot->host, ios);
-- 
1.8.4

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