[PATCH v3 3/3] RISC-V: Ensure Zicbom has a valid block size

[Conor.Dooley at microchip.com]

On 29/11/2022 19:45, Conor Dooley wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Hey Drew,
> 
> On Tue, Nov 29, 2022 at 03:34:47PM +0100, Andrew Jones wrote:
>> When a DT puts zicbom in the isa string, but does not provide a block
>> size, ALT_CMO_OP() will attempt to do cache operations on address
>> zero since the start address will be ANDed with zero. We can't simply
>> BUG() in riscv_init_cbom_blocksize() when we fail to find a block
>> size because the failure will happen before logging works, leaving
>> users to scratch their heads as to why the boot hung. Instead, ensure
>> Zicbom is disabled and output an error which will hopefully alert
>> people that the DT needs to be fixed. While at it, add a check that
>> the block size is a power-of-2 too.
>>
>> Signed-off-by: Andrew Jones <ajones at ventanamicro.com>
>> Reviewed-by: Conor Dooley <conor.dooley at microchip.com>
> 
> This seems to be failing on nommu :/ I've got host machines issues so I
> could not reproduce it for you lcoally and paste an actual log, but if
> you build rv64_nommu_virt_defconfig I think you should be able to
> reproduce.

The actual error is:
riscv64-unknown-linux-gnu-ld: arch/riscv/kernel/cpufeature.o: in function `.L0 ':
cpufeature.c:(.text.unlikely+0x8): undefined reference to `riscv_cbom_block_size'


> 
> Thanks,
> Conor.
> 
>> Reviewed-by: Heiko Stuebner <heiko at sntech.de>
>> ---
>>   arch/riscv/kernel/cpufeature.c | 13 +++++++++++++
>>   1 file changed, 13 insertions(+)
>>
>> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
>> index 220be7222129..93e45560af30 100644
>> --- a/arch/riscv/kernel/cpufeature.c
>> +++ b/arch/riscv/kernel/cpufeature.c
>> @@ -9,6 +9,7 @@
>>   #include <linux/bitmap.h>
>>   #include <linux/ctype.h>
>>   #include <linux/libfdt.h>
>> +#include <linux/log2.h>
>>   #include <linux/module.h>
>>   #include <linux/of.h>
>>   #include <asm/alternative.h>
>> @@ -70,6 +71,18 @@ EXPORT_SYMBOL_GPL(__riscv_isa_extension_available);
>>
>>   static bool riscv_isa_extension_check(int id)
>>   {
>> +     switch (id) {
>> +     case RISCV_ISA_EXT_ZICBOM:
>> +             if (!riscv_cbom_block_size) {
>> +                     pr_err("Zicbom detected in ISA string, but no cbom-block-size found\n");
>> +                     return false;
>> +             } else if (!is_power_of_2(riscv_cbom_block_size)) {
>> +                     pr_err("cbom-block-size present, but is not a power-of-2\n");
>> +                     return false;
>> +             }
>> +             return true;
>> +     }
>> +
>>        return true;
>>   }
>>
>> --
>> 2.38.1
>>
>>
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> 
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