[PATCH 3/9] lib: sbi_emulate_csr: Utilize platform hooks for unknown CSRs

[Vivian Wang]

On 3/28/24 22:11, Christoph Müllner wrote:
> [adding the list]

Oops! Thanks a lot for catching that

Vivian "dram"

>
> On Wed, Mar 27, 2024 at 12:22 PM Vivian Wang <uwu at dram.page> wrote:
>> On 3/27/24 18:11, Christoph Müllner wrote:
>>> In case we trap during CSR accesses, we have a few defined CSRs
>>> that are gracefully emulated. In case we don't know what to do
>>> with an unknown CSR, let's give the platform a chance to handle
>>> the CSR access.
>> This seems to be a pretty awful way to handle this. Can we use a vendor
>> SBI extension [1] instead? It would be far easier to implement and also
>> easier for users to use and probe for suppport.
>>
>> Also, the C910 manual mentions a sxstatus register that is partly RO and
>> partly RW in Supervisor mode. Can we just use that instead?
> Yes, I'll switch to sxstatus (I was not aware of this CSR).
> Thanks!
>
>> [1] https://github.com/riscv-non-isa/riscv-sbi-doc/blob/master/src/ext-vendor.adoc
>> [2] https://github.com/T-head-Semi/openc910/blob/main/doc/%E7%8E%84%E9%93%81C910%E7%94%A8%E6%88%B7%E6%89%8B%E5%86%8C.pdf
>>
>> Vivian "dram"
>>> Signed-off-by: Christoph Müllner <christoph.muellner at vrull.eu>
>>> ---
>>>  lib/sbi/sbi_emulate_csr.c | 8 ++++++--
>>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/lib/sbi/sbi_emulate_csr.c b/lib/sbi/sbi_emulate_csr.c
>>> index 5f3b111..a6cb855 100644
>>> --- a/lib/sbi/sbi_emulate_csr.c
>>> +++ b/lib/sbi/sbi_emulate_csr.c
>>> @@ -14,6 +14,7 @@
>>>  #include <sbi/sbi_emulate_csr.h>
>>>  #include <sbi/sbi_error.h>
>>>  #include <sbi/sbi_hart.h>
>>> +#include <sbi/sbi_platform.h>
>>>  #include <sbi/sbi_scratch.h>
>>>  #include <sbi/sbi_timer.h>
>>>  #include <sbi/sbi_trap.h>
>>> @@ -147,7 +148,8 @@ int sbi_emulate_csr_read(int csr_num, struct sbi_trap_regs *regs,
>>>  #undef switchcase_hpm
>>>
>>>       default:
>>> -             ret = SBI_ENOTSUPP;
>>> +             ret = sbi_platform_read_csr(sbi_platform_ptr(scratch),
>>> +                                         csr_num, regs, csr_val);
>>>               break;
>>>       }
>>>
>>> @@ -162,6 +164,7 @@ int sbi_emulate_csr_write(int csr_num, struct sbi_trap_regs *regs,
>>>                         ulong csr_val)
>>>  {
>>>       int ret = 0;
>>> +     struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
>>>       ulong prev_mode = (regs->mstatus & MSTATUS_MPP) >> MSTATUS_MPP_SHIFT;
>>>  #if __riscv_xlen == 32
>>>       bool virt = (regs->mstatusH & MSTATUSH_MPV) ? true : false;
>>> @@ -185,7 +188,8 @@ int sbi_emulate_csr_write(int csr_num, struct sbi_trap_regs *regs,
>>>               break;
>>>  #endif
>>>       default:
>>> -             ret = SBI_ENOTSUPP;
>>> +             ret = sbi_platform_write_csr(sbi_platform_ptr(scratch),
>>> +                                          csr_num, regs, csr_val);
>>>               break;
>>>       }
>>>
>>