lkml.org 
[lkml]   [2018]   [May]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v6 05/10] drivers: qcom: rpmh-rsc: write sleep/wake requests to TCS
On Fri, Apr 27 2018 at 17:24 -0600, Doug Anderson wrote:
>Hi,
>
>On Fri, Apr 27, 2018 at 2:54 PM, Matthias Kaehlcke <mka@chromium.org> wrote:
>>> > Am I getting something wrong here?
>>>
>>> The for_each_set_bit() should increment the 'i' and we would attempt to
>>> compare the first address in the request with the next command in the
>>> TCS cache. If they don't match we repeat the process again. If it does,
>>> then we loop through 'j' to find if the sequence matches.
>>>
>>> Did I miss something?
>>
>> One of us is clearly in need of more caffeine or ready for the
>> weekend, it might be me :) Maybe another pair of eyeballs could help
I need them both. Sorry about the back and forth. I understand what the
problem is. The code doesnt look right. I seem to have messed it up.
Thanks Matthias for being patient and going through this.

>> to resolve this deadlock ...
>>
>> My single stepping above assumes that tcs->cmd_cache[i] matches
>> cmd[0].addr, i.e. we either found the start of the sequence we are
>> looking for or another sequence that starts with the same address. My
>> claim is that the code returns i in either case, whether the
>> subsequent addresses match or not.
>
>I haven't reviewed this patch in detail, but I attempted to be another
>pair of eyes here. Something is definitely wrong with the "for (j =
>0; j < len; j++)" loop. I believe the code that's written right now
>is equivalent to this much shorter function:
>
>+static int find_match(const struct tcs_group *tcs, const struct tcs_cmd *cmd,
>+ int len)
>+{
>+ int i, j;
>+
>+ /* Check for already cached commands */
>+ for_each_set_bit(i, tcs->slots, MAX_TCS_SLOTS) {
>+ if (tcs->cmd_cache[i] == cmd[0].addr)
>+ return i;
>+ }
>+
>+ return -ENODATA;
>+}
>
>Specifically the test "if (tcs->cmd_cache[i] != cmd[0].addr)" does not
>take "j" into account. Thus if it was false when "j == 0" it will
>continue to be false for "j == 1", "j == 2", etc. Eventually you'll
>hit the "else if (j == len - 1)" and return.
>
>I believe that's what Matthias has been saying. I personally haven't
>looked at the rest of the patch to see how things out to be fixed, but
>I'm quite convinced that the function either has a bug or should be
>written as the shorter version I've written above.
>
Yes, this is incorrect in its current form. This is what it should be -

static int find_match(const struct tcs_group *tcs, const struct tcs_cmd *cmd,
int len)
{
int i, j;

/* Check for already cached commands */
for_each_set_bit(i, tcs->slots, MAX_TCS_SLOTS) {
if (tcs->cmd_cache[i] != cmd[0].addr)
continue;
for (j = 0; j < len; j++) {
WARN(tcs->cmd_cache[i + j] != cmd[j].addr,
"Message does not match previous sequence.\n");
return -EINVAL;
}
if (j == len - 1)
return i;
}

return -ENODATA;
}


Thanks,
Lina

\
 
 \ /
  Last update: 2018-05-01 18:18    [W:0.355 / U:0.396 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site