linux-kernel - [PATCH 2/3] usb: chipidea: Simplify Tegra DMA alignment code

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Date:   Sat, 23 Sep 2023 21:41:56 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Peter Chen <peter.chen@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Geis <pgwipeout@...il.com>,
        Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <treding@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-usb@...r.kernel.org
Subject: [PATCH 2/3] usb: chipidea: Simplify Tegra DMA alignment code

The USB host on Tegra3 works with DWORD alignment. Previous code tried
to align the buffer, but it did align the wrapper struct instead, so
the buffer was at a constant offset of 8 bytes (two pointers) from
assumed alignment.  Since kmalloc() guarantees at least 8-byte
alignment, the alignment-extending is removed.

Fixes: fc53d5279094 ("usb: chipidea: tegra: Support host mode")
Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
---
 drivers/usb/chipidea/host.c | 45 +++++++++++++++----------------------
 1 file changed, 18 insertions(+), 27 deletions(-)

diff --git a/drivers/usb/chipidea/host.c b/drivers/usb/chipidea/host.c
index abddd39d1ff1..0cce19208370 100644
--- a/drivers/usb/chipidea/host.c
+++ b/drivers/usb/chipidea/host.c
@@ -30,8 +30,7 @@ struct ehci_ci_priv {
 };
 
 struct ci_hdrc_dma_aligned_buffer {
-	void *kmalloc_ptr;
-	void *old_xfer_buffer;
+	void *original_buffer;
 	u8 data[];
 };
 
@@ -380,60 +379,52 @@ static int ci_ehci_bus_suspend(struct usb_hcd *hcd)
 	return 0;
 }
 
-static void ci_hdrc_free_dma_aligned_buffer(struct urb *urb)
+static void ci_hdrc_free_dma_aligned_buffer(struct urb *urb, bool copy_back)
 {
 	struct ci_hdrc_dma_aligned_buffer *temp;
-	size_t length;
 
 	if (!(urb->transfer_flags & URB_ALIGNED_TEMP_BUFFER))
 		return;
+	urb->transfer_flags &= ~URB_ALIGNED_TEMP_BUFFER;
 
 	temp = container_of(urb->transfer_buffer,
 			    struct ci_hdrc_dma_aligned_buffer, data);
+	urb->transfer_buffer = temp->original_buffer;
+
+	if (copy_back && usb_urb_dir_in(urb)) {
+		size_t length;
 
-	if (usb_urb_dir_in(urb)) {
 		if (usb_pipeisoc(urb->pipe))
 			length = urb->transfer_buffer_length;
 		else
 			length = urb->actual_length;
 
-		memcpy(temp->old_xfer_buffer, temp->data, length);
+		memcpy(temp->original_buffer, temp->data, length);
 	}
-	urb->transfer_buffer = temp->old_xfer_buffer;
-	kfree(temp->kmalloc_ptr);
 
-	urb->transfer_flags &= ~URB_ALIGNED_TEMP_BUFFER;
+	kfree(temp);
 }
 
 static int ci_hdrc_alloc_dma_aligned_buffer(struct urb *urb, gfp_t mem_flags)
 {
-	struct ci_hdrc_dma_aligned_buffer *temp, *kmalloc_ptr;
-	const unsigned int ci_hdrc_usb_dma_align = 32;
-	size_t kmalloc_size;
+	struct ci_hdrc_dma_aligned_buffer *temp;
 
 	if (urb->num_sgs || urb->sg || urb->transfer_buffer_length == 0)
 		return 0;
-	if (!((uintptr_t)urb->transfer_buffer & (ci_hdrc_usb_dma_align - 1)) && !(urb->transfer_buffer_length & 3))
+	if (IS_ALIGNED((uintptr_t)urb->transfer_buffer, 4)
+	    && IS_ALIGNED(urb->transfer_buffer_length, 4))
 		return 0;
 
-	/* Allocate a buffer with enough padding for alignment */
-	kmalloc_size = ALIGN(urb->transfer_buffer_length, 4) +
-		       sizeof(struct ci_hdrc_dma_aligned_buffer) +
-		       ci_hdrc_usb_dma_align - 1;
-
-	kmalloc_ptr = kmalloc(kmalloc_size, mem_flags);
-	if (!kmalloc_ptr)
+	temp = kmalloc(sizeof(*temp) + ALIGN(urb->transfer_buffer_length, 4), mem_flags);
+	if (!temp)
 		return -ENOMEM;
 
-	/* Position our struct dma_aligned_buffer such that data is aligned */
-	temp = PTR_ALIGN(kmalloc_ptr + 1, ci_hdrc_usb_dma_align) - 1;
-	temp->kmalloc_ptr = kmalloc_ptr;
-	temp->old_xfer_buffer = urb->transfer_buffer;
 	if (usb_urb_dir_out(urb))
 		memcpy(temp->data, urb->transfer_buffer,
 		       urb->transfer_buffer_length);
+
+	temp->original_buffer = urb->transfer_buffer;
 	urb->transfer_buffer = temp->data;
-
 	urb->transfer_flags |= URB_ALIGNED_TEMP_BUFFER;
 
 	return 0;
@@ -450,7 +441,7 @@ static int ci_hdrc_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
 
 	ret = usb_hcd_map_urb_for_dma(hcd, urb, mem_flags);
 	if (ret)
-		ci_hdrc_free_dma_aligned_buffer(urb);
+		ci_hdrc_free_dma_aligned_buffer(urb, false);
 
 	return ret;
 }
@@ -458,7 +449,7 @@ static int ci_hdrc_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
 static void ci_hdrc_unmap_urb_for_dma(struct usb_hcd *hcd, struct urb *urb)
 {
 	usb_hcd_unmap_urb_for_dma(hcd, urb);
-	ci_hdrc_free_dma_aligned_buffer(urb);
+	ci_hdrc_free_dma_aligned_buffer(urb, true);
 }
 
 #ifdef CONFIG_PM_SLEEP
-- 
2.39.2