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mmc: sdhci-of-at91: Implement specific ->set_clock() function
Disabling the internal clock while configuring the SD card clock can lead to internal clock stabilization issue and/or unexpected switch to the base clock when using presets. A quirk SDHCI_QUIRK2_NEED_DELAY_AFTER_INT_CLK_RST was introduced to fix these bugs. The cause was assumed to be a too long internal re-synchronisation but it seems in some cases the delay (even if longer) doesn't fix this bug. The safest workaround is to not disable/enable the internal clock during the SD card clock configuration. Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com> Acked-by: Adrian Hunter <adrian.hunter@intel.com> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
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@ -15,6 +15,7 @@
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*/
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#include <linux/clk.h>
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#include <linux/delay.h>
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#include <linux/err.h>
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#include <linux/io.h>
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#include <linux/mmc/host.h>
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@ -37,8 +38,52 @@ struct sdhci_at91_priv {
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struct clk *mainck;
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};
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static void sdhci_at91_set_clock(struct sdhci_host *host, unsigned int clock)
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{
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u16 clk;
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unsigned long timeout;
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host->mmc->actual_clock = 0;
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/*
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* There is no requirement to disable the internal clock before
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* changing the SD clock configuration. Moreover, disabling the
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* internal clock, changing the configuration and re-enabling the
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* internal clock causes some bugs. It can prevent to get the internal
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* clock stable flag ready and an unexpected switch to the base clock
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* when using presets.
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*/
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clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
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clk &= SDHCI_CLOCK_INT_EN;
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sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
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if (clock == 0)
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return;
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clk = sdhci_calc_clk(host, clock, &host->mmc->actual_clock);
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clk |= SDHCI_CLOCK_INT_EN;
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sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
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/* Wait max 20 ms */
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timeout = 20;
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while (!((clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL))
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& SDHCI_CLOCK_INT_STABLE)) {
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if (timeout == 0) {
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pr_err("%s: Internal clock never stabilised.\n",
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mmc_hostname(host->mmc));
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return;
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}
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timeout--;
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mdelay(1);
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}
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clk |= SDHCI_CLOCK_CARD_EN;
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sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
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}
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static const struct sdhci_ops sdhci_at91_sama5d2_ops = {
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.set_clock = sdhci_set_clock,
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.set_clock = sdhci_at91_set_clock,
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.set_bus_width = sdhci_set_bus_width,
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.reset = sdhci_reset,
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.set_uhs_signaling = sdhci_set_uhs_signaling,
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@ -46,7 +91,6 @@ static const struct sdhci_ops sdhci_at91_sama5d2_ops = {
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static const struct sdhci_pltfm_data soc_data_sama5d2 = {
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.ops = &sdhci_at91_sama5d2_ops,
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.quirks2 = SDHCI_QUIRK2_NEED_DELAY_AFTER_INT_CLK_RST,
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};
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static const struct of_device_id sdhci_at91_dt_match[] = {
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