[U-Boot] unused-const-variable warnings in FSL DDR driver

[Thomas Schaefer]

>>
>>> On 02/09/2017 02:32 AM, Thomas Schaefer wrote:
>>>> Hi York,
>>>>
>>>>
>>>>
>>>> When compiling latest u-boot with gcc 6.3 compiler, I get several 
>>>> 'unused-const-variable' warnings in options.c file of FSL DDR driver.
>>>> Affected variables are for (DIMM_SLOTS_PER_CTLR==2) configuration (e.g.
>>>> dual_0S[4]) and warnings could be fixed with the patch applied.
>>>>
>>>>
>>>>
>>>> What do you think?
>>>
>>> Thomas,
>>>
>>> Thanks for bringing it to my attention. I understand GCC 6 may have 
>>> more warnings. The proposed patch is OK in logic but it increases the 
>>> size of code unnecessarily. Can you come up with a different fix?
>>>
>>> I can come back to check after I finish my work on hand.
>>>
>>> York
>>
>> Hi York,
>>
>> not sure if I understand this correctly, but why is code size 
>> increased when these variables are not defined? I think code size is 
>> decreased instead as these variables are no longer defined if not needed.
>>
>> I also don't see a way to achieve this in a different way as the 
>> variables are defined differently for DDR2, DDR3 and DDR4.
>>
>>

>Wait a minute, did you generate the patch backward? Your patch shows
>removing "#if CONFIG_DIMM_SLOTS_PER_CTLR==2" which doesn't exist in
>current code. If the logic is reversed, then yes, you are reducing the size. Can 
>GCC 6 optimize out the unused data? If yes, maybe we can use __maybe_unused
>to get rid of the warning?
>
>York

Oops, you are right, sorry for the confusion. Here's the corrected version:

diff --git a/drivers/ddr/fsl/options.c b/drivers/ddr/fsl/options.c
index d6a8fcb216..d90ed0b6cc 100644
--- a/drivers/ddr/fsl/options.c
+++ b/drivers/ddr/fsl/options.c
@@ -89,6 +89,7 @@ static const struct dynamic_odt single_S[4] = {
        {0, 0, 0, 0},
 };

+#if (CONFIG_DIMM_SLOTS_PER_CTLR==2)
 static const struct dynamic_odt dual_DD[4] = {
        {       /* cs0 */
                FSL_DDR_ODT_NEVER,
@@ -235,6 +236,7 @@ static const struct dynamic_odt dual_0S[4] = {
        {0, 0, 0, 0}

 };
+#endif

 static const struct dynamic_odt odt_unknown[4] = {
        {       /* cs0 */
@@ -319,6 +321,7 @@ static const struct dynamic_odt single_S[4] = {
        {0, 0, 0, 0},
 };

+#if (CONFIG_DIMM_SLOTS_PER_CTLR==2)
 static const struct dynamic_odt dual_DD[4] = {
        {       /* cs0 */
                FSL_DDR_ODT_NEVER,
@@ -465,6 +468,7 @@ static const struct dynamic_odt dual_0S[4] = {
        {0, 0, 0, 0}

 };
+#endif

 static const struct dynamic_odt odt_unknown[4] = {
        {       /* cs0 */
@@ -529,6 +533,7 @@ static const struct dynamic_odt single_S[4] = {
        {0, 0, 0, 0},
 };

+#if (CONFIG_DIMM_SLOTS_PER_CTLR==2)
 static const struct dynamic_odt dual_DD[4] = {
        {       /* cs0 */
                FSL_DDR_ODT_OTHER_DIMM,
@@ -676,6 +681,7 @@ static const struct dynamic_odt dual_0S[4] = {
        {0, 0, 0, 0}

 };
+#endif

 static const struct dynamic_odt odt_unknown[4] = {
        {       /* cs0 */


Best regards,
Thomas
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