Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758195AbaJ3GhK (ORCPT ); Thu, 30 Oct 2014 02:37:10 -0400 Received: from mail-gw1-out.broadcom.com ([216.31.210.62]:60240 "EHLO mail-gw1-out.broadcom.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758137AbaJ3GhG (ORCPT ); Thu, 30 Oct 2014 02:37:06 -0400 X-IronPort-AV: E=Sophos;i="5.07,284,1413270000"; d="scan'208";a="49699556" From: Scott Branden To: Ulf Hansson , Russell King , Peter Griffin , Stephen Warren , Chris Ball , Piotr Krol CC: , , Joe Perches , , Ray Jui , , Scott Branden Subject: [PATCHv2 3/5] mmc: shdci-bcm2835: add efficient back-to-back write workaround Date: Wed, 29 Oct 2014 23:36:55 -0700 Message-ID: <1414651017-3545-4-git-send-email-sbranden@broadcom.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1414651017-3545-1-git-send-email-sbranden@broadcom.com> References: <1414651017-3545-1-git-send-email-sbranden@broadcom.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The bcm2835 has clock domain issues when back to back writes to certain registers are written. The existing driver works around this issue with udelay. A more efficient method is to store the 8 and 16 bit writes to the registers affected and then write them as 32 bits at the appropriate time. Signed-off-by: Scott Branden --- drivers/mmc/host/sdhci-bcm2835.c | 103 ++++++++++++++++++++------------------ 1 file changed, 55 insertions(+), 48 deletions(-) diff --git a/drivers/mmc/host/sdhci-bcm2835.c b/drivers/mmc/host/sdhci-bcm2835.c index b6cb365..f8c450a 100644 --- a/drivers/mmc/host/sdhci-bcm2835.c +++ b/drivers/mmc/host/sdhci-bcm2835.c @@ -24,34 +24,9 @@ #include #include "sdhci-pltfm.h" -/* - * 400KHz is max freq for card ID etc. Use that as min card clock. We need to - * know the min to enable static calculation of max BCM2835_SDHCI_WRITE_DELAY. - */ -#define MIN_FREQ 400000 - -/* - * The Arasan has a bugette whereby it may lose the content of successive - * writes to registers that are within two SD-card clock cycles of each other - * (a clock domain crossing problem). It seems, however, that the data - * register does not have this problem, which is just as well - otherwise we'd - * have to nobble the DMA engine too. - * - * This should probably be dynamically calculated based on the actual card - * frequency. However, this is the longest we'll have to wait, and doesn't - * seem to slow access down too much, so the added complexity doesn't seem - * worth it for now. - * - * 1/MIN_FREQ is (max) time per tick of eMMC clock. - * 2/MIN_FREQ is time for two ticks. - * Multiply by 1000000 to get uS per two ticks. - * *1000000 for uSecs. - * +1 for hack rounding. - */ -#define BCM2835_SDHCI_WRITE_DELAY (((2 * 1000000) / MIN_FREQ) + 1) - -struct bcm2835_sdhci { - u32 shadow; +struct bcm2835_sdhci_host { + u32 shadow_cmd; + u32 shadow_blk; }; #define REG_OFFSET_IN_BITS(reg) ((reg) << 3 & 0x18) @@ -80,33 +55,71 @@ static u8 bcm2835_sdhci_readb(struct sdhci_host *host, int reg) return byte; } -static void bcm2835_sdhci_writel(struct sdhci_host *host, u32 val, int reg) +static inline void bcm2835_sdhci_writel(struct sdhci_host *host, + u32 val, int reg) { writel(val, host->ioaddr + reg); - - udelay(BCM2835_SDHCI_WRITE_DELAY); } - +/* + * The Arasan has a bugette whereby it may lose the content of successive + * writes to the same register that are within two SD-card clock cycles of + * each other (a clock domain crossing problem). The data + * register does not have this problem, which is just as well - otherwise we'd + * have to nobble the DMA engine too. + * + * This wouldn't be a problem with the code except that we can only write the + * controller with 32-bit writes. So two different 16-bit registers are + * written back to back creates the problem. + * + * In reality, this only happens when SDHCI_BLOCK_SIZE and SDHCI_BLOCK_COUNT + * are written followed by SDHCI_TRANSFER_MODE and SDHCI_COMMAND. + * The BLOCK_SIZE and BLOCK_COUNT are meaningless until a command issued so + * the work around can be further optimized. We can keep shadow values of + * BLOCK_SIZE, BLOCK_COUNT, and TRANSFER_MODE until a COMMAND is issued. + * Then, write the BLOCK_SIZE+BLOCK_COUNT in a single 32-bit write followed + * by the TRANSFER+COMMAND in another 32-bit write. + */ static void bcm2835_sdhci_writew(struct sdhci_host *host, u16 val, int reg) { struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host); - struct bcm2835_sdhci *bcm2835_host = pltfm_host->priv; - u32 oldval = (reg == SDHCI_COMMAND) ? bcm2835_host->shadow : - bcm2835_sdhci_readl(host, reg & ~3); + struct bcm2835_sdhci_host *bcm2835_host = pltfm_host->priv; u32 word_shift = REG_OFFSET_IN_BITS(reg); u32 mask = 0xffff << word_shift; - u32 newval = (oldval & ~mask) | (val << word_shift); - - if (reg == SDHCI_TRANSFER_MODE) - bcm2835_host->shadow = newval; - else + u32 oldval, newval; + + if (reg == SDHCI_COMMAND) { + /* Write the block now as we are issuing a command */ + if (bcm2835_host->shadow_blk != 0) { + bcm2835_sdhci_writel(host, bcm2835_host->shadow_blk, + SDHCI_BLOCK_SIZE); + bcm2835_host->shadow_blk = 0; + } + oldval = bcm2835_host->shadow_cmd; + } else if (reg == SDHCI_BLOCK_SIZE || reg == SDHCI_BLOCK_COUNT) { + /* Block size and count are stored in shadow reg */ + oldval = bcm2835_host->shadow_blk; + } else { + /* Read reg, all other registers are not shadowed */ + oldval = readl(host->ioaddr + (reg & ~3)); + } + newval = (oldval & ~mask) | (val << word_shift); + + if (reg == SDHCI_TRANSFER_MODE) { + /* Save the transfer mode until the command is issued */ + bcm2835_host->shadow_cmd = newval; + } else if (reg == SDHCI_BLOCK_SIZE || reg == SDHCI_BLOCK_COUNT) { + /* Save the block info until the command is issued */ + bcm2835_host->shadow_blk = newval; + } else { + /* Command or other regular 32-bit write */ bcm2835_sdhci_writel(host, newval, reg & ~3); + } } static void bcm2835_sdhci_writeb(struct sdhci_host *host, u8 val, int reg) { - u32 oldval = bcm2835_sdhci_readl(host, reg & ~3); + u32 oldval = readl(host->ioaddr + (reg & ~3)); u32 byte_shift = REG_OFFSET_IN_BITS(reg); u32 mask = 0xff << byte_shift; u32 newval = (oldval & ~mask) | (val << byte_shift); @@ -114,11 +127,6 @@ static void bcm2835_sdhci_writeb(struct sdhci_host *host, u8 val, int reg) bcm2835_sdhci_writel(host, newval, reg & ~3); } -static unsigned int bcm2835_sdhci_get_min_clock(struct sdhci_host *host) -{ - return MIN_FREQ; -} - static const struct sdhci_ops bcm2835_sdhci_ops = { .read_l = bcm2835_sdhci_readl, .read_w = bcm2835_sdhci_readw, @@ -128,7 +136,6 @@ static const struct sdhci_ops bcm2835_sdhci_ops = { .write_b = bcm2835_sdhci_writeb, .set_clock = sdhci_set_clock, .get_max_clock = sdhci_pltfm_clk_get_max_clock, - .get_min_clock = bcm2835_sdhci_get_min_clock, .set_bus_width = sdhci_set_bus_width, .reset = sdhci_reset, .set_uhs_signaling = sdhci_set_uhs_signaling, @@ -143,7 +150,7 @@ static const struct sdhci_pltfm_data bcm2835_sdhci_pdata = { static int bcm2835_sdhci_probe(struct platform_device *pdev) { struct sdhci_host *host; - struct bcm2835_sdhci *bcm2835_host; + struct bcm2835_sdhci_host *bcm2835_host; struct sdhci_pltfm_host *pltfm_host; int ret; -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/