lkml.org 
[lkml]   [2021]   [Dec]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 4.19 29/74] clk: qcom: regmap-mux: fix parent clock lookup
From
On 15/12/2021 12:16, Pavel Machek wrote:
> Hi!
>
>> The function mux_get_parent() uses qcom_find_src_index() to find the
>> parent clock index, which is incorrect: qcom_find_src_index() uses src
>> enum for the lookup, while mux_get_parent() should use cfg field (which
>> corresponds to the register value). Add qcom_find_cfg_index() function
>> doing this kind of lookup and use it for mux parent lookup.
>
> This appears to have problems with error handling.
>
>> +++ b/drivers/clk/qcom/clk-regmap-mux.c
>> @@ -36,7 +36,7 @@ static u8 mux_get_parent(struct clk_hw *
>> val &= mask;
>>
>> if (mux->parent_map)
>> - return qcom_find_src_index(hw, mux->parent_map, val);
>> + return qcom_find_cfg_index(hw, mux->parent_map, val);
>>
>> return val;
>> }
>
> So this returns u8.
>
>> +int qcom_find_cfg_index(struct clk_hw *hw, const struct parent_map *map, u8 cfg)
>> +{
>> + int i, num_parents = clk_hw_get_num_parents(hw);
>> +
>> + for (i = 0; i < num_parents; i++)
>> + if (cfg == map[i].cfg)
>> + return i;
>> +
>> + return -ENOENT;
>> +}
>
> In case of error, -ENOENT will be cast to u8 in caller. I don't
> believe that is correct.

Unfortunately there is no way to return proper error code from
clk_ops->get_parent() callback. However returning -ENOENT would
translate to 254. Then clk_core_get_parent_by_index() would determine
that there is no such parent and return NULL. A call to clk_set_parent
would reparent the clock.

Returning some sensible default (e.g. 0) would be much worse, since then
the clock subsystem would assume that the clock has correct parent. A
call to clk_set_parent would always result in ops->set_parent() call,
reparenting the clock correctly.

Most probably it would be correct to make ops->get_parent() return int
instead of u8 (either an index or an -ERROR). However this was out of
scope for this patch.

--
With best wishes
Dmitry

\
 
 \ /
  Last update: 2021-12-15 11:37    [W:0.073 / U:0.520 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site