mmc: queue: let host controllers specify maximum discard timeout

Some host controllers will not operate without a hardware
timeout that is limited in value.  However large discards
require large timeouts, so there needs to be a way to
specify the maximum discard size.

A host controller driver may now specify the maximum discard
timeout possible so that max_discard_sectors can be calculated.

However, for eMMC when the High Capacity Erase Group Size
is not in use, the timeout calculation depends on clock
rate which may change.  For that case Preferred Erase Size
is used instead.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 76 insertions, 0 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 7843efe22359..ac82865b8c2f 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1516,6 +1516,82 @@ int mmc_erase_group_aligned(struct mmc_card *card, unsigned int from,
 }
 EXPORT_SYMBOL(mmc_erase_group_aligned);
 
+static unsigned int mmc_do_calc_max_discard(struct mmc_card *card,
+					    unsigned int arg)
+{
+	struct mmc_host *host = card->host;
+	unsigned int max_discard, x, y, qty = 0, max_qty, timeout;
+	unsigned int last_timeout = 0;
+
+	if (card->erase_shift)
+		max_qty = UINT_MAX >> card->erase_shift;
+	else if (mmc_card_sd(card))
+		max_qty = UINT_MAX;
+	else
+		max_qty = UINT_MAX / card->erase_size;
+
+	/* Find the largest qty with an OK timeout */
+	do {
+		y = 0;
+		for (x = 1; x && x <= max_qty && max_qty - x >= qty; x <<= 1) {
+			timeout = mmc_erase_timeout(card, arg, qty + x);
+			if (timeout > host->max_discard_to)
+				break;
+			if (timeout < last_timeout)
+				break;
+			last_timeout = timeout;
+			y = x;
+		}
+		qty += y;
+	} while (y);
+
+	if (!qty)
+		return 0;
+
+	if (qty == 1)
+		return 1;
+
+	/* Convert qty to sectors */
+	if (card->erase_shift)
+		max_discard = --qty << card->erase_shift;
+	else if (mmc_card_sd(card))
+		max_discard = qty;
+	else
+		max_discard = --qty * card->erase_size;
+
+	return max_discard;
+}
+
+unsigned int mmc_calc_max_discard(struct mmc_card *card)
+{
+	struct mmc_host *host = card->host;
+	unsigned int max_discard, max_trim;
+
+	if (!host->max_discard_to)
+		return UINT_MAX;
+
+	/*
+	 * Without erase_group_def set, MMC erase timeout depends on clock
+	 * frequence which can change.  In that case, the best choice is
+	 * just the preferred erase size.
+	 */
+	if (mmc_card_mmc(card) && !(card->ext_csd.erase_group_def & 1))
+		return card->pref_erase;
+
+	max_discard = mmc_do_calc_max_discard(card, MMC_ERASE_ARG);
+	if (mmc_can_trim(card)) {
+		max_trim = mmc_do_calc_max_discard(card, MMC_TRIM_ARG);
+		if (max_trim < max_discard)
+			max_discard = max_trim;
+	} else if (max_discard < card->erase_size) {
+		max_discard = 0;
+	}
+	pr_debug("%s: calculated max. discard sectors %u for timeout %u ms\n",
+		 mmc_hostname(host), max_discard, host->max_discard_to);
+	return max_discard;
+}
+EXPORT_SYMBOL(mmc_calc_max_discard);
+
 int mmc_set_blocklen(struct mmc_card *card, unsigned int blocklen)
 {
 	struct mmc_command cmd = {0};