netdev - [PATCH net-next 1/6] net: ipa: use an array for transactions

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Date:   Wed, 31 Aug 2022 17:40:12 -0500
From:   Alex Elder <elder@...aro.org>
To:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com
Cc:     mka@...omium.org, evgreen@...omium.org, bjorn.andersson@...aro.org,
        quic_cpratapa@...cinc.com, quic_avuyyuru@...cinc.com,
        quic_jponduru@...cinc.com, quic_subashab@...cinc.com,
        elder@...nel.org, netdev@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net-next 1/6] net: ipa: use an array for transactions

Transactions are always allocated one at a time.  The maximum number
of them we could ever need occurs if each TRE is assigned to a
transaction.  So a channel requires no more transactions than the
number of TREs in its transfer ring.  That number is known to be a
power-of-2 less than 65536.

The transaction pool abstraction is used for other things, but for
transactions we can use a simple array of transaction structures,
and use a free index to indicate which entry in the array is the
next one free for allocation.

By having the number of elements in the array be a power-of-2, we
can use an ever-incrementing 16-bit free index, and use it modulo
the array size.  Distinguish a "trans_id" (whose value can exceed
the number of entries in the transaction array) from a "trans_index"
(which is less than the number of entries).

Signed-off-by: Alex Elder <elder@...aro.org>
---
 drivers/net/ipa/gsi.h       |  4 +++-
 drivers/net/ipa/gsi_trans.c | 39 +++++++++++++++++++++----------------
 2 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/drivers/net/ipa/gsi.h b/drivers/net/ipa/gsi.h
index 23de5f67374cf..4a88aec7e7d92 100644
--- a/drivers/net/ipa/gsi.h
+++ b/drivers/net/ipa/gsi.h
@@ -82,7 +82,9 @@ struct gsi_trans_pool {
 
 struct gsi_trans_info {
 	atomic_t tre_avail;		/* TREs available for allocation */
-	struct gsi_trans_pool pool;	/* transaction pool */
+
+	u16 free_id;			/* first free trans in array */
+	struct gsi_trans *trans;	/* transaction array */
 	struct gsi_trans **map;		/* TRE -> transaction map */
 
 	struct gsi_trans_pool sg_pool;	/* scatterlist pool */
diff --git a/drivers/net/ipa/gsi_trans.c b/drivers/net/ipa/gsi_trans.c
index 18e7e8c405bea..9775e50d0423f 100644
--- a/drivers/net/ipa/gsi_trans.c
+++ b/drivers/net/ipa/gsi_trans.c
@@ -343,20 +343,22 @@ struct gsi_trans *gsi_channel_trans_alloc(struct gsi *gsi, u32 channel_id,
 	struct gsi_channel *channel = &gsi->channel[channel_id];
 	struct gsi_trans_info *trans_info;
 	struct gsi_trans *trans;
+	u16 trans_index;
 
 	if (WARN_ON(tre_count > channel->trans_tre_max))
 		return NULL;
 
 	trans_info = &channel->trans_info;
 
-	/* We reserve the TREs now, but consume them at commit time.
-	 * If there aren't enough available, we're done.
-	 */
+	/* If we can't reserve the TREs for the transaction, we're done */
 	if (!gsi_trans_tre_reserve(trans_info, tre_count))
 		return NULL;
 
-	/* Allocate and initialize non-zero fields in the transaction */
-	trans = gsi_trans_pool_alloc(&trans_info->pool, 1);
+	trans_index = trans_info->free_id % channel->tre_count;
+	trans = &trans_info->trans[trans_index];
+	memset(trans, 0, sizeof(*trans));
+
+	/* Initialize non-zero fields in the transaction */
 	trans->gsi = gsi;
 	trans->channel_id = channel_id;
 	trans->rsvd_count = tre_count;
@@ -367,15 +369,17 @@ struct gsi_trans *gsi_channel_trans_alloc(struct gsi *gsi, u32 channel_id,
 	sg_init_marker(trans->sgl, tre_count);
 
 	trans->direction = direction;
-
-	spin_lock_bh(&trans_info->spinlock);
-
-	list_add_tail(&trans->links, &trans_info->alloc);
-
-	spin_unlock_bh(&trans_info->spinlock);
-
 	refcount_set(&trans->refcount, 1);
 
+	/* This free transaction will now be allocated */
+	trans_info->free_id++;
+
+	spin_lock_bh(&trans_info->spinlock);
+
+	list_add_tail(&trans->links, &trans_info->alloc);
+
+	spin_unlock_bh(&trans_info->spinlock);
+
 	return trans;
 }
 
@@ -736,10 +740,11 @@ int gsi_channel_trans_init(struct gsi *gsi, u32 channel_id)
 	 * modulo that number to determine the next one that's free.
 	 * Transactions are allocated one at a time.
 	 */
-	ret = gsi_trans_pool_init(&trans_info->pool, sizeof(struct gsi_trans),
-				  tre_max, 1);
-	if (ret)
+	trans_info->trans = kcalloc(tre_count, sizeof(*trans_info->trans),
+				    GFP_KERNEL);
+	if (!trans_info->trans)
 		return -ENOMEM;
+	trans_info->free_id = 0;	/* modulo channel->tre_count */
 
 	/* A completion event contains a pointer to the TRE that caused
 	 * the event (which will be the last one used by the transaction).
@@ -777,7 +782,7 @@ int gsi_channel_trans_init(struct gsi *gsi, u32 channel_id)
 err_map_free:
 	kfree(trans_info->map);
 err_trans_free:
-	gsi_trans_pool_exit(&trans_info->pool);
+	kfree(trans_info->trans);
 
 	dev_err(gsi->dev, "error %d initializing channel %u transactions\n",
 		ret, channel_id);
@@ -791,6 +796,6 @@ void gsi_channel_trans_exit(struct gsi_channel *channel)
 	struct gsi_trans_info *trans_info = &channel->trans_info;
 
 	gsi_trans_pool_exit(&trans_info->sg_pool);
-	gsi_trans_pool_exit(&trans_info->pool);
+	kfree(trans_info->trans);
 	kfree(trans_info->map);
 }
-- 
2.34.1