From: Andrew Jeffery andrew@aj.id.au
[ Upstream commit 9f4c2b516b4f031e3cd0e45957f4150b3c1a083d ]
Subtracting the offset delta from four-byte alignment lead to wrapping of the requested length where `count` is less than `off`. Generalise the length handling to enable and optimise aligned access sizes for all offset and size combinations. The new formula produces the following results for given offset and count values:
offset count | length --------------+------- 0 1 | 1 0 2 | 2 0 3 | 2 0 4 | 4 0 5 | 4 1 1 | 1 1 2 | 1 1 3 | 1 1 4 | 1 1 5 | 1 2 1 | 1 2 2 | 2 2 3 | 2 2 4 | 2 2 5 | 2 3 1 | 1 3 2 | 1 3 3 | 1 3 4 | 1 3 5 | 1
We might need something like this for the cfam chardevs as well, for example we don't currently implement any alignment restrictions / handling in the hardware master driver.
Signed-off-by: Andrew Jeffery andrew@aj.id.au Signed-off-by: Joel Stanley joel@jms.id.au Link: https://lore.kernel.org/r/20191108051945.7109-6-joel@jms.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/fsi/fsi-core.c | 31 +++++++++++++++++++++++++++---- 1 file changed, 27 insertions(+), 4 deletions(-)
diff --git a/drivers/fsi/fsi-core.c b/drivers/fsi/fsi-core.c index 4ea63d9bd131..8feca59c1f6b 100644 --- a/drivers/fsi/fsi-core.c +++ b/drivers/fsi/fsi-core.c @@ -419,6 +419,31 @@ static int fsi_slave_scan(struct fsi_slave *slave) return 0; }
+static unsigned long aligned_access_size(size_t offset, size_t count) +{ + unsigned long offset_unit, count_unit; + + /* Criteria: + * + * 1. Access size must be less than or equal to the maximum access + * width or the highest power-of-two factor of offset + * 2. Access size must be less than or equal to the amount specified by + * count + * + * The access width is optimal if we can calculate 1 to be strictly + * equal while still satisfying 2. + */ + + /* Find 1 by the bottom bit of offset (with a 4 byte access cap) */ + offset_unit = BIT(__builtin_ctzl(offset | 4)); + + /* Find 2 by the top bit of count */ + count_unit = BIT(8 * sizeof(unsigned long) - 1 - __builtin_clzl(count)); + + /* Constrain the maximum access width to the minimum of both criteria */ + return BIT(__builtin_ctzl(offset_unit | count_unit)); +} + static ssize_t fsi_slave_sysfs_raw_read(struct file *file, struct kobject *kobj, struct bin_attribute *attr, char *buf, loff_t off, size_t count) @@ -434,8 +459,7 @@ static ssize_t fsi_slave_sysfs_raw_read(struct file *file, return -EINVAL;
for (total_len = 0; total_len < count; total_len += read_len) { - read_len = min_t(size_t, count, 4); - read_len -= off & 0x3; + read_len = aligned_access_size(off, count - total_len);
rc = fsi_slave_read(slave, off, buf + total_len, read_len); if (rc) @@ -462,8 +486,7 @@ static ssize_t fsi_slave_sysfs_raw_write(struct file *file, return -EINVAL;
for (total_len = 0; total_len < count; total_len += write_len) { - write_len = min_t(size_t, count, 4); - write_len -= off & 0x3; + write_len = aligned_access_size(off, count - total_len);
rc = fsi_slave_write(slave, off, buf + total_len, write_len); if (rc)