drm/amdgpu: Simplify RAS EEPROM checksum calculations

Rename update_table_header() to
write_table_header() as this function is actually
writing it to EEPROM.

Use kernel types; use u8 to carry around the
checksum, in order to take advantage of arithmetic
modulo 8-bits (256).

Tidy up to 80 columns.

When updating the checksum, just recalculate the
whole thing.

Cc: Alexander Deucher <Alexander.Deucher@amd.com>
Cc: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Acked-by: Alexander Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.c
index 7d0f9e1..54ef315 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.c
@@ -141,8 +141,8 @@ static void __decode_table_header_from_buff(struct amdgpu_ras_eeprom_table_heade
        hdr->checksum         = le32_to_cpu(pp[4]);
 }
 
-static int __update_table_header(struct amdgpu_ras_eeprom_control *control,
-                                unsigned char *buff)
+static int __write_table_header(struct amdgpu_ras_eeprom_control *control,
+                               unsigned char *buff)
 {
        int ret = 0;
        struct amdgpu_device *adev = to_amdgpu_device(control);
@@ -162,69 +162,74 @@ static int __update_table_header(struct amdgpu_ras_eeprom_control *control,
        return ret;
 }
 
-static uint32_t  __calc_hdr_byte_sum(struct amdgpu_ras_eeprom_control *control)
+static u8 __calc_hdr_byte_sum(const struct amdgpu_ras_eeprom_control *control)
 {
        int i;
-       uint32_t tbl_sum = 0;
+       u8 hdr_sum = 0;
+       u8  *p;
+       size_t sz;
 
        /* Header checksum, skip checksum field in the calculation */
-       for (i = 0; i < sizeof(control->tbl_hdr) - sizeof(control->tbl_hdr.checksum); i++)
-               tbl_sum += *(((unsigned char *)&control->tbl_hdr) + i);
+       sz = sizeof(control->tbl_hdr) - sizeof(control->tbl_hdr.checksum);
+       p = (u8 *) &control->tbl_hdr;
+       for (i = 0; i < sz; i++, p++)
+               hdr_sum += *p;
 
-       return tbl_sum;
+       return hdr_sum;
 }
 
-static uint32_t  __calc_recs_byte_sum(struct eeprom_table_record *records,
-                                     int num)
+static u8 __calc_recs_byte_sum(const struct eeprom_table_record *record,
+                              const int num)
 {
        int i, j;
-       uint32_t tbl_sum = 0;
+       u8  tbl_sum = 0;
+
+       if (!record)
+               return 0;
 
        /* Records checksum */
        for (i = 0; i < num; i++) {
-               struct eeprom_table_record *record = &records[i];
+               u8 *p = (u8 *) &record[i];
 
-               for (j = 0; j < sizeof(*record); j++) {
-                       tbl_sum += *(((unsigned char *)record) + j);
-               }
+               for (j = 0; j < sizeof(*record); j++, p++)
+                       tbl_sum += *p;
        }
 
        return tbl_sum;
 }
 
-static inline uint32_t  __calc_tbl_byte_sum(struct amdgpu_ras_eeprom_control *control,
-                                 struct eeprom_table_record *records, int num)
+static inline u8
+__calc_tbl_byte_sum(struct amdgpu_ras_eeprom_control *control,
+                   struct eeprom_table_record *records, int num)
 {
-       return __calc_hdr_byte_sum(control) + __calc_recs_byte_sum(records, num);
+       return __calc_hdr_byte_sum(control) +
+               __calc_recs_byte_sum(records, num);
 }
 
-/* Checksum = 256 -((sum of all table entries) mod 256) */
 static void __update_tbl_checksum(struct amdgpu_ras_eeprom_control *control,
-                                 struct eeprom_table_record *records, int num,
-                                 uint32_t old_hdr_byte_sum)
+                                 struct eeprom_table_record *records, int num)
 {
-       /*
-        * This will update the table sum with new records.
-        *
-        * TODO: What happens when the EEPROM table is to be wrapped around
-        * and old records from start will get overridden.
-        */
-
-       /* need to recalculate updated header byte sum */
-       control->tbl_byte_sum -= old_hdr_byte_sum;
-       control->tbl_byte_sum += __calc_tbl_byte_sum(control, records, num);
+       u8 v;
 
-       control->tbl_hdr.checksum = 256 - (control->tbl_byte_sum % 256);
+       control->tbl_byte_sum = __calc_tbl_byte_sum(control, records, num);
+       /* Avoid 32-bit sign extension. */
+       v = -control->tbl_byte_sum;
+       control->tbl_hdr.checksum = v;
 }
 
-/* table sum mod 256 + checksum must equals 256 */
-static bool __validate_tbl_checksum(struct amdgpu_ras_eeprom_control *control,
-                           struct eeprom_table_record *records, int num)
+static bool __verify_tbl_checksum(struct amdgpu_ras_eeprom_control *control,
+                                 struct eeprom_table_record *records,
+                                 int num)
 {
+       u8 result;
+
        control->tbl_byte_sum = __calc_tbl_byte_sum(control, records, num);
 
-       if (control->tbl_hdr.checksum + (control->tbl_byte_sum % 256) != 256) {
-               DRM_WARN("Checksum mismatch, checksum: %u ", control->tbl_hdr.checksum);
+       result = (u8)control->tbl_hdr.checksum + control->tbl_byte_sum;
+       if (result) {
+               DRM_WARN("RAS table checksum mismatch: stored:0x%02X wants:0x%02hhX",
+                        control->tbl_hdr.checksum,
+                        -control->tbl_byte_sum);
                return false;
        }
 
@@ -232,8 +237,8 @@ static bool __validate_tbl_checksum(struct amdgpu_ras_eeprom_control *control,
 }
 
 static int amdgpu_ras_eeprom_correct_header_tag(
-                               struct amdgpu_ras_eeprom_control *control,
-                               uint32_t header)
+       struct amdgpu_ras_eeprom_control *control,
+       uint32_t header)
 {
        unsigned char buff[RAS_TABLE_HEADER_SIZE];
        struct amdgpu_ras_eeprom_table_header *hdr = &control->tbl_hdr;
@@ -243,7 +248,7 @@ static int amdgpu_ras_eeprom_correct_header_tag(
 
        mutex_lock(&control->tbl_mutex);
        hdr->header = header;
-       ret = __update_table_header(control, buff);
+       ret = __write_table_header(control, buff);
        mutex_unlock(&control->tbl_mutex);
 
        return ret;
@@ -262,11 +267,9 @@ int amdgpu_ras_eeprom_reset_table(struct amdgpu_ras_eeprom_control *control)
        hdr->first_rec_offset = RAS_RECORD_START;
        hdr->tbl_size = RAS_TABLE_HEADER_SIZE;
 
-       control->tbl_byte_sum = 0;
-       __update_tbl_checksum(control, NULL, 0, 0);
+       __update_tbl_checksum(control, NULL, 0);
        control->next_addr = RAS_RECORD_START;
-
-       ret = __update_table_header(control, buff);
+       ret = __write_table_header(control, buff);
 
        mutex_unlock(&control->tbl_mutex);
 
@@ -521,8 +524,6 @@ static int amdgpu_ras_eeprom_xfer(struct amdgpu_ras_eeprom_control *control,
        }
 
        if (write) {
-               uint32_t old_hdr_byte_sum = __calc_hdr_byte_sum(control);
-
                /*
                 * Update table header with size and CRC and account for table
                 * wrap around where the assumption is that we treat it as empty
@@ -537,10 +538,9 @@ static int amdgpu_ras_eeprom_xfer(struct amdgpu_ras_eeprom_control *control,
                        control->tbl_hdr.tbl_size = RAS_TABLE_HEADER_SIZE +
                        control->num_recs * RAS_TABLE_RECORD_SIZE;
 
-               __update_tbl_checksum(control, records, num, old_hdr_byte_sum);
-
-               __update_table_header(control, buffs);
-       } else if (!__validate_tbl_checksum(control, records, num)) {
+               __update_tbl_checksum(control, records, num);
+               __write_table_header(control, buffs);
+       } else if (!__verify_tbl_checksum(control, records, num)) {
                DRM_WARN("EEPROM Table checksum mismatch!");
                /* TODO Uncomment when EEPROM read/write is relliable */
                /* ret = -EIO; */

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.h
index fa9c509..4906ed9 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.h
@@ -48,7 +48,7 @@ struct amdgpu_ras_eeprom_control {
        uint32_t next_addr;
        unsigned int num_recs;
        struct mutex tbl_mutex;
-       uint32_t tbl_byte_sum;
+       u8 tbl_byte_sum;
 };
 
 /*