[v8,2/3] platform/x86/amd/pmc: Handle overflow cases where the num_samples range is higher

Commit Message

Shyam Sundar S K Oct. 10, 2023, 2:50 p.m. UTC

In amd_pmc_stb_debugfs_open_v2(), the stb buffer is created based on the
num_samples and the read/write pointer offset. This holds good when the
num_samples reported by PMFW is less than S2D_TELEMETRY_BYTES_MAX; where
the stb buffer gets filled from 0th position until
S2D_TELEMETRY_BYTES_MAX - 1 based on the read/write pointer offset.

But when the num_samples exceeds the S2D_TELEMETRY_BYTES_MAX, the current
code does not handle it well as it does not account for the cases where
the stb buffer has to filled up as a circular buffer.

Handle this scenario into two cases, where first memcpy will have the
samples from location:
(num_samples % S2D_TELEMETRY_BYTES_MAX) - (S2D_TELEMETRY_BYTES_MAX - 1)
and next memcpy will have the newest ones i.e.
0 - (num_samples % S2D_TELEMETRY_BYTES_MAX - 1)

Suggested-by: Hans de Goede <[e-mail]>
Reviewed-by: Hans de Goede <[e-mail]>
Signed-off-by: Sanket Goswami <[e-mail]>
Signed-off-by: Shyam Sundar S K <[e-mail]>
---
v7->v8:
- No change

v6->v7:
- No change

v5->v6:
 - Make changes as per Hans on v5
 - based on review-ilpo branch

v4->v5:
 - Fix exisiting code problems when reading stb buffer as a circular data
 - based on review-ilpo branch

v3->v4:
 - Update code branches and commit-msg as per Ilpo's remark.

v2->v3:
 - no change

v1->v2:
 - rebase to 'review-hans' branch
 - drop 2/4 of v1
   (https://patchwork.kernel.org/project/platform-driver-x86/list/?series=775324&state=%2A&archive=both)

 drivers/platform/x86/amd/pmc/pmc.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

Patch

diff --git a/drivers/platform/x86/amd/pmc/pmc.c b/drivers/platform/x86/amd/pmc/pmc.c
index 609bad470fe3..e190ec5a602f 100644
--- a/drivers/platform/x86/amd/pmc/pmc.c
+++ b/drivers/platform/x86/amd/pmc/pmc.c
@@ -276,16 +276,23 @@  static int amd_pmc_stb_debugfs_open_v2(struct inode *inode, struct file *filp)
 
 	flex_arr->size = fsize;
 
-	/* Start capturing data from the last push location */
+	/*
+	 * Start capturing data from the last push location.
+	 * This is for general cases, where the stb limits
+	 * are meant for standard usage.
+	 */
 	if (num_samples > S2D_TELEMETRY_BYTES_MAX) {
-		fsize  = S2D_TELEMETRY_BYTES_MAX;
-		stb_rdptr_offset = num_samples - fsize;
+		/* First read oldest data starting 1 behind last write till end of ringbuffer */
+		stb_rdptr_offset = num_samples % S2D_TELEMETRY_BYTES_MAX;
+		fsize = S2D_TELEMETRY_BYTES_MAX - stb_rdptr_offset;
+
+		memcpy_fromio(flex_arr->data, dev->stb_virt_addr + stb_rdptr_offset, fsize);
+		/* Second copy the newer samples from offset 0 - last write */
+		memcpy_fromio(flex_arr->data + fsize, dev->stb_virt_addr, stb_rdptr_offset);
 	} else {
-		fsize = num_samples;
-		stb_rdptr_offset = 0;
+		memcpy_fromio(flex_arr->data, dev->stb_virt_addr, fsize);
 	}
 
-	memcpy_fromio(flex_arr->data, dev->stb_virt_addr + stb_rdptr_offset, fsize);
 	filp->private_data = flex_arr;
 
 	return 0;