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author | Andrew Jeffery <andrew@aj.id.au> | 2019-11-08 08:19:39 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-12-31 18:35:55 +0300 |
commit | 7664c4a25b3776ff5036f5fdcd54c34e2d2cddb8 (patch) | |
tree | 39dca1256bc2653b1632ba770dc66adae145d085 | |
parent | 2f75e5391abd8f9fa65bfdd9ad05c93e90bf5a58 (diff) | |
download | linux-7664c4a25b3776ff5036f5fdcd54c34e2d2cddb8.tar.xz |
fsi: core: Fix small accesses and unaligned offsets via sysfs
[ 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>
-rw-r--r-- | drivers/fsi/fsi-core.c | 31 |
1 files changed, 27 insertions, 4 deletions
diff --git a/drivers/fsi/fsi-core.c b/drivers/fsi/fsi-core.c index 2c31563fdcae..c6fa9b393e84 100644 --- a/drivers/fsi/fsi-core.c +++ b/drivers/fsi/fsi-core.c @@ -552,6 +552,31 @@ 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) @@ -567,8 +592,7 @@ 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) @@ -595,8 +619,7 @@ 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) |