platform/x86/amd/pmc: Handle overflow cases where the num_samples range is higher

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 <hdegoede@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sanket Goswami <Sanket.Goswami@amd.com>
Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Link: https://lore.kernel.org/r/20231010145003.139932-2-Shyam-sundar.S-k@amd.com
[ij: renamed flex_arr -> stb_data_arr]
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

diff --git a/drivers/platform/x86/amd/pmc/pmc.c b/drivers/platform/x86/amd/pmc/pmc.c
index 77dca9a1f00f57ad8e3a3c04f9065f97a954e5f4..bc254e1fa71a5784b73377acd16096ff23b85d87 100644 (file)
--- 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)
 
        stb_data_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(stb_data_arr->data, dev->stb_virt_addr + stb_rdptr_offset, fsize);
+               /* Second copy the newer samples from offset 0 - last write */
+               memcpy_fromio(stb_data_arr->data + fsize, dev->stb_virt_addr, stb_rdptr_offset);
        } else {
-               fsize = num_samples;
-               stb_rdptr_offset = 0;
+               memcpy_fromio(stb_data_arr->data, dev->stb_virt_addr, fsize);
        }
 
-       memcpy_fromio(stb_data_arr->data, dev->stb_virt_addr + stb_rdptr_offset, fsize);
        filp->private_data = stb_data_arr;
 
        return 0;