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bcm2835-sdhost: Firmware manages the clock divisor
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The bcm2835-sdhost driver hands control of the CDIV clock divisor
register to matching firmware, allowing it to adjust to a changing
core clock. This removes the need to use the performance governor or
to enable io_is_busy on the on-demand governor in order to get the
best SD performance.

N.B. As SD clocks must be an integer divisor of the core clock, it is
possible that the SD clock for "turbo" mode can be different (even
lower) than "normal" mode.

Signed-off-by: Phil Elwell <[email protected]>
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Phil Elwell committed Apr 11, 2016
1 parent a2fb5ae commit dff460c
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Showing 2 changed files with 87 additions and 49 deletions.
135 changes: 86 additions & 49 deletions drivers/mmc/host/bcm2835-sdhost.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,7 @@
#include <linux/of_dma.h>
#include <linux/time.h>
#include <linux/workqueue.h>
#include <soc/bcm2835/raspberrypi-firmware.h>

#define DRIVER_NAME "sdhost-bcm2835"

Expand Down Expand Up @@ -190,6 +191,8 @@ struct bcm2835_host {
unsigned int use_sbc:1; /* Send CMD23 */

unsigned int debug:1; /* Enable debug output */
unsigned int firmware_sets_cdiv:1; /* Let the firmware manage the clock */
unsigned int reset_clock:1; /* Reset the clock fore the next request */

/*DMA part*/
struct dma_chan *dma_chan_rxtx; /* DMA channel for reads and writes */
Expand Down Expand Up @@ -437,7 +440,7 @@ static void bcm2835_sdhost_reset_internal(struct bcm2835_host *host)
host->clock = 0;
host->sectors = 0;
bcm2835_sdhost_write(host, host->hcfg, SDHCFG);
bcm2835_sdhost_write(host, host->cdiv, SDCDIV);
bcm2835_sdhost_write(host, SDCDIV_MAX_CDIV, SDCDIV);
mmiowb();
}

Expand Down Expand Up @@ -1510,6 +1513,7 @@ void bcm2835_sdhost_set_clock(struct bcm2835_host *host, unsigned int clock)
{
int div = 0; /* Initialized for compiler warning */
unsigned int input_clock = clock;
unsigned long flags;

if (host->debug)
pr_info("%s: set_clock(%d)\n", mmc_hostname(host->mmc), clock);
Expand Down Expand Up @@ -1541,62 +1545,84 @@ void bcm2835_sdhost_set_clock(struct bcm2835_host *host, unsigned int clock)

host->mmc->actual_clock = 0;

if (clock < 100000) {
/* Can't stop the clock, but make it as slow as possible
* to show willing
*/
host->cdiv = SDCDIV_MAX_CDIV;
bcm2835_sdhost_write(host, host->cdiv, SDCDIV);
return;
}
if (host->firmware_sets_cdiv) {
u32 msg[3] = { clock, 0, 0 };

div = host->max_clk / clock;
if (div < 2)
div = 2;
if ((host->max_clk / div) > clock)
div++;
div -= 2;
rpi_firmware_property(rpi_firmware_get(NULL),
RPI_FIRMWARE_SET_SDHOST_CLOCK,
&msg, sizeof(msg));

if (div > SDCDIV_MAX_CDIV)
div = SDCDIV_MAX_CDIV;
clock = max(msg[1], msg[2]);
spin_lock_irqsave(&host->lock, flags);
} else {
spin_lock_irqsave(&host->lock, flags);
if (clock < 100000) {
/* Can't stop the clock, but make it as slow as
* possible to show willing
*/
host->cdiv = SDCDIV_MAX_CDIV;
bcm2835_sdhost_write(host, host->cdiv, SDCDIV);
mmiowb();
spin_unlock_irqrestore(&host->lock, flags);
return;
}

clock = host->max_clk / (div + 2);
host->mmc->actual_clock = clock;
div = host->max_clk / clock;
if (div < 2)
div = 2;
if ((host->max_clk / div) > clock)
div++;
div -= 2;

if (div > SDCDIV_MAX_CDIV)
div = SDCDIV_MAX_CDIV;

clock = host->max_clk / (div + 2);

host->cdiv = div;
bcm2835_sdhost_write(host, host->cdiv, SDCDIV);

if (host->debug)
pr_info("%s: clock=%d -> max_clk=%d, cdiv=%x "
"(actual clock %d)\n",
mmc_hostname(host->mmc), input_clock,
host->max_clk, host->cdiv,
clock);
}

/* Calibrate some delays */

host->ns_per_fifo_word = (1000000000/clock) *
((host->mmc->caps & MMC_CAP_4_BIT_DATA) ? 8 : 32);

if (clock > input_clock) {
/* Save the closest value, to make it easier
to reduce in the event of error */
host->overclock_50 = (clock/MHZ);
if (input_clock == 50 * MHZ) {
if (clock > input_clock) {
/* Save the closest value, to make it easier
to reduce in the event of error */
host->overclock_50 = (clock/MHZ);

if (clock != host->overclock) {
pr_warn("%s: overclocking to %dHz\n",
mmc_hostname(host->mmc), clock);
host->overclock = clock;
if (clock != host->overclock) {
pr_warn("%s: overclocking to %dHz\n",
mmc_hostname(host->mmc), clock);
host->overclock = clock;
}
} else if (host->overclock) {
host->overclock = 0;
if (clock == 50 * MHZ)
pr_warn("%s: cancelling overclock\n",
mmc_hostname(host->mmc));
}
}
else if (host->overclock)
{
host->overclock = 0;
if (clock == 50 * MHZ)
pr_warn("%s: cancelling overclock\n",
mmc_hostname(host->mmc));
}

host->cdiv = div;
bcm2835_sdhost_write(host, host->cdiv, SDCDIV);

/* Set the timeout to 500ms */
bcm2835_sdhost_write(host, host->mmc->actual_clock/2, SDTOUT);
bcm2835_sdhost_write(host, clock/2, SDTOUT);

if (host->debug)
pr_info("%s: clock=%d -> max_clk=%d, cdiv=%x (actual clock %d)\n",
mmc_hostname(host->mmc), input_clock,
host->max_clk, host->cdiv, host->mmc->actual_clock);
host->mmc->actual_clock = clock;
host->clock = input_clock;
host->reset_clock = 0;

mmiowb();
spin_unlock_irqrestore(&host->lock, flags);
}

static void bcm2835_sdhost_request(struct mmc_host *mmc, struct mmc_request *mrq)
Expand Down Expand Up @@ -1645,6 +1671,9 @@ static void bcm2835_sdhost_request(struct mmc_host *mmc, struct mmc_request *mrq
(mrq->data->blocks > host->pio_limit))
bcm2835_sdhost_prepare_dma(host, mrq->data);

if (host->reset_clock)
bcm2835_sdhost_set_clock(host, host->clock);

spin_lock_irqsave(&host->lock, flags);

WARN_ON(host->mrq != NULL);
Expand Down Expand Up @@ -1711,11 +1740,6 @@ static void bcm2835_sdhost_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)

log_event("IOS<", ios->clock, 0);

if (!ios->clock || ios->clock != host->clock) {
bcm2835_sdhost_set_clock(host, ios->clock);
host->clock = ios->clock;
}

/* set bus width */
host->hcfg &= ~SDHCFG_WIDE_EXT_BUS;
if (ios->bus_width == MMC_BUS_WIDTH_4)
Expand All @@ -1731,6 +1755,9 @@ static void bcm2835_sdhost_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
mmiowb();

spin_unlock_irqrestore(&host->lock, flags);

if (!ios->clock || ios->clock != host->clock)
bcm2835_sdhost_set_clock(host, ios->clock);
}

static struct mmc_host_ops bcm2835_sdhost_ops = {
Expand Down Expand Up @@ -1802,7 +1829,7 @@ static void bcm2835_sdhost_tasklet_finish(unsigned long param)
host->overclock_50--;
pr_warn("%s: reducing overclock due to errors\n",
mmc_hostname(host->mmc));
bcm2835_sdhost_set_clock(host,50*MHZ);
host->reset_clock = 1;
mrq->cmd->error = -EILSEQ;
mrq->cmd->retries = 1;
}
Expand Down Expand Up @@ -1959,6 +1986,7 @@ static int bcm2835_sdhost_probe(struct platform_device *pdev)
struct resource *iomem;
struct bcm2835_host *host;
struct mmc_host *mmc;
u32 msg[3];
int ret;

pr_debug("bcm2835_sdhost_probe\n");
Expand All @@ -1970,7 +1998,6 @@ static int bcm2835_sdhost_probe(struct platform_device *pdev)
mmc->ops = &bcm2835_sdhost_ops;
host = mmc_priv(mmc);
host->mmc = mmc;
host->cmd_quick_poll_retries = 0;
host->pio_timeout = msecs_to_jiffies(500);
host->pio_limit = 1;
host->max_delay = 1; /* Warn if over 1ms */
Expand Down Expand Up @@ -2059,6 +2086,16 @@ static int bcm2835_sdhost_probe(struct platform_device *pdev)
else
mmc->caps |= MMC_CAP_4_BIT_DATA;

msg[0] = 0;
msg[1] = ~0;
msg[2] = ~0;

rpi_firmware_property(rpi_firmware_get(NULL),
RPI_FIRMWARE_SET_SDHOST_CLOCK,
&msg, sizeof(msg));

host->firmware_sets_cdiv = (msg[1] != ~0);

ret = bcm2835_sdhost_add_host(host);
if (ret)
goto err;
Expand Down
1 change: 1 addition & 0 deletions include/soc/bcm2835/raspberrypi-firmware.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -76,6 +76,7 @@ enum rpi_firmware_property_tag {
RPI_FIRMWARE_SET_VOLTAGE = 0x00038003,
RPI_FIRMWARE_SET_TURBO = 0x00038009,
RPI_FIRMWARE_SET_CUSTOMER_OTP = 0x00038021,
RPI_FIRMWARE_SET_SDHOST_CLOCK = 0x00038042,

/* Dispmanx TAGS */
RPI_FIRMWARE_FRAMEBUFFER_ALLOCATE = 0x00040001,
Expand Down

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