[Skiboot] [PATCH 14/15] libstb/drivers: Add ROM code driver
cclaudio at linux.vnet.ibm.com
Thu Sep 8 01:53:33 AEST 2016
On 09/03/2016 12:38 AM, Oliver O'Halloran wrote:
> On Thu, Aug 11, 2016 at 3:23 PM, Claudio Carvalho
> <cclaudio at linux.vnet.ibm.com> wrote:
>> + /**
>> + * We use memcpy_ci to copy the verification code from the secure ROM
>> + * to memory. Due to performance issues we opted to run it from memory.
>> + */
>> + chip = next_chip(NULL);
>> + xscom_read(chip->id, reg_addr, ®_data);
>> + memcpy_ci(romcode_base_addr, (void*) reg_data,
>> + ROMCODE_MEMORY_SIZE);
> Could you document why accessing the ROM needs to be done with CI
> loads? We use them when dealing with MMIO registers (like the XSCOMs)
> to ensure loads and stores go to/from the actual register rather than
> the cache, but I don't see why this is necessary for a ROM.
Sure. I can replace the comments above by something like this:
* The logic that contains the ROM within the processor is implemented
* in a way that it only responds to CI (cache inhibited) operations.
* Due to performance issues we copy the verification code from the
* secure ROM to memory and we use memcpy_ci to do that.
Is that better?
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