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fsi: core: Fix small accesses and unaligned offsets via sysfs

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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>
This commit is contained in:
Andrew Jeffery 2019-11-08 15:49:39 +10:30 committed by Greg Kroah-Hartman
parent ae77481601
commit 9f4c2b516b
1 changed files with 27 additions and 4 deletions
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31
drivers/fsi/fsi-core.c
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@ -544,6 +544,31 @@ 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)
@ -559,8 +584,7 @@ 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)
@ -587,8 +611,7 @@ 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)