[PATCH mmc-next] mmc: allow setting slot index via device tree alias

[Matthias Schiffer <matthias.schiffer@ew.tq-group.com>]

As with GPIO, UART and others, allow specifying the device index via the
aliases node in the device tree.

On embedded devices, there is often a combination of removable (e.g.
SD card) and non-removable MMC devices (e.g. eMMC).
Therefore the index might change depending on

* host of removable device
* removable card present or not

This makes it difficult to hardcode the root device, if it is on the
non-removable device. E.g. if SD card is present eMMC will be mmcblk1,
if SD card is not present at boot, eMMC will be mmcblk0.

All indices defined in the aliases node will be reserved for use by the
respective MMC device, moving the indices of devices that don't have an
alias up into the non-reserved range. If the aliases node is not found,
the driver will act as before.

This is a rebased and slightly cleaned up version of
https://www.spinics.net/lists/linux-mmc/msg26588.html .

Based-on-patch-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Link: https://lkml.org/lkml/2020/8/5/194
---
 drivers/mmc/core/block.c | 13 +++++++++++--
 drivers/mmc/core/core.c  | 38 ++++++++++++++++++++++++++++++++++++++
 drivers/mmc/core/core.h  |  3 +++
 drivers/mmc/core/host.c  | 15 +++++++++++++--
 4 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
index 7896952de1ac..4620afaf0e50 100644
--- a/drivers/mmc/core/block.c
+++ b/drivers/mmc/core/block.c
@@ -38,6 +38,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/idr.h>
 #include <linux/debugfs.h>
+#include <linux/of.h>
 
 #include <linux/mmc/ioctl.h>
 #include <linux/mmc/card.h>
@@ -2260,9 +2261,17 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
 					      int area_type)
 {
 	struct mmc_blk_data *md;
-	int devidx, ret;
+	int rsvidx, devidx = -1, ret;
+
+	rsvidx = mmc_get_reserved_index(card->host);
+	if (rsvidx >= 0)
+		devidx = ida_simple_get(&mmc_blk_ida, rsvidx, rsvidx + 1,
+					GFP_KERNEL);
+	if (devidx < 0)
+		devidx = ida_simple_get(&mmc_blk_ida,
+					mmc_first_nonreserved_index(),
+					max_devices, GFP_KERNEL);
 
-	devidx = ida_simple_get(&mmc_blk_ida, 0, max_devices, GFP_KERNEL);
 	if (devidx < 0) {
 		/*
 		 * We get -ENOSPC because there are no more any available
diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 8ccae6452b9c..39aca8adacd1 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -2419,10 +2419,48 @@ void mmc_unregister_pm_notifier(struct mmc_host *host)
 }
 #endif
 
+static int mmc_max_reserved_idx = -1;
+
+/**
+ * mmc_first_nonreserved_index() - get the first index that is not reserved
+ */
+int mmc_first_nonreserved_index(void)
+{
+	return mmc_max_reserved_idx + 1;
+}
+
+/**
+ * mmc_get_reserved_index() - get the index reserved for this MMC host
+ *
+ * Returns:
+ *   The index reserved for this host on success,
+ *   negative error if no index is reserved for this host
+ */
+int mmc_get_reserved_index(struct mmc_host *host)
+{
+	return of_alias_get_id(host->parent->of_node, "mmc");
+}
+
+static void __init mmc_of_reserve_idx(void)
+{
+	int max;
+
+	max = of_alias_get_highest_id("mmc");
+	if (max < 0)
+		return;
+
+	mmc_max_reserved_idx = max;
+
+	pr_debug("MMC: reserving %d slots for OF aliases\n",
+		 mmc_max_reserved_idx + 1);
+}
+
 static int __init mmc_init(void)
 {
 	int ret;
 
+	mmc_of_reserve_idx();
+
 	ret = mmc_register_bus();
 	if (ret)
 		return ret;
diff --git a/drivers/mmc/core/core.h b/drivers/mmc/core/core.h
index 575ac0257af2..6aef6cf4e90f 100644
--- a/drivers/mmc/core/core.h
+++ b/drivers/mmc/core/core.h
@@ -79,6 +79,9 @@ int mmc_attach_mmc(struct mmc_host *host);
 int mmc_attach_sd(struct mmc_host *host);
 int mmc_attach_sdio(struct mmc_host *host);
 
+int mmc_first_nonreserved_index(void);
+int mmc_get_reserved_index(struct mmc_host *host);
+
 /* Module parameters */
 extern bool use_spi_crc;
 
diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
index ce43f7573d80..386e15afde83 100644
--- a/drivers/mmc/core/host.c
+++ b/drivers/mmc/core/host.c
@@ -387,6 +387,7 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
 {
 	int err;
 	struct mmc_host *host;
+	int alias_id, min_idx, max_idx;
 
 	host = kzalloc(sizeof(struct mmc_host) + extra, GFP_KERNEL);
 	if (!host)
@@ -395,7 +396,18 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
 	/* scanning will be enabled when we're ready */
 	host->rescan_disable = 1;
 
-	err = ida_simple_get(&mmc_host_ida, 0, 0, GFP_KERNEL);
+	host->parent = dev;
+
+	alias_id = mmc_get_reserved_index(host);
+	if (alias_id >= 0) {
+		min_idx = alias_id;
+		max_idx = alias_id + 1;
+	} else {
+		min_idx = mmc_first_nonreserved_index();
+		max_idx = 0;
+	}
+
+	err = ida_simple_get(&mmc_host_ida, min_idx, max_idx, GFP_KERNEL);
 	if (err < 0) {
 		kfree(host);
 		return NULL;
@@ -406,7 +418,6 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
 	dev_set_name(&host->class_dev, "mmc%d", host->index);
 	host->ws = wakeup_source_register(NULL, dev_name(&host->class_dev));
 
-	host->parent = dev;
 	host->class_dev.parent = dev;
 	host->class_dev.class = &mmc_host_class;
 	device_initialize(&host->class_dev);
-- 
2.17.1