On Thu, Jun 14, 2012 at 10:09:07AM +0200, Jean Delvare wrote: > On Thu, 14 Jun 2012 14:14:30 +0800, Xiao, Hui wrote: > > From your "good example of a valid case" above. I believe we might have different > > understanding of the "Bit Width" field. > > > > Just to make sure, do you take "Bit Width" here(1 bit) as the bit length one should > > got for mask /*after*/ shifting bit offset(31 bit) of the access_width(32 bit) > > one read from the register(length unknown, or should equal to access length?) ? > > > > That's why you think: > > bit_width + bit_offset <= *access_bit_width > > is valid. > > I am not Gary, but it is also how I read the specification. Thanks, Jean. It seemed like the correct interpretation to me. > > > For me I take "Bit Width" as bits of the register for access boundary, > > so I think: > > (*access_bit_width <= bit_width) && (bit_offset < *access_bit_width) > > is valid. This is not the check that the patch contains. It also does not verify that an access will read or write all of the register bits. > > > > For you above case, personally I saw you got a 1-bit register, but want to > > read 32bit from it, and want to get bit[31] by shifting 31bit and mask 0x1. > > > > Please correct me if I am wrong. Not sure which should be the case ACPI SPEC > > expected. I also have not found any specific explanation on these assumption. > > What makes me believe Gary is right is the granularity of each field. > bit_width and bit_offset can be set with a 1-bit granularity, while > access_bit_width can only be 8, 16, 32 or 64. This clearly means that > access_bit_width (and Access Size before that) is a hardware thing, > while bit_width and bit_offset can only be software things. You've > never seen I/O ports that can be read 3 or 5 bits at a time... The "<= Access Size" in this diagram will hopefully clarify the "bit_width + bit_offset <= *access_bit_width" check: |<------------------ <= Access Size ----------------->| |<-- Register Bit Width -->|<-- Register Bit Offset -->| |<--------------------- Access Size --------------------->| ^ | Address --+ The case described in the patch header looks like: |<-- Register Bit Width (64) -->|<-- Register Bit Offset (0) -->| |<-------+------>|<----------- Access Size (32)---------------->| | ^ +-- **neglected register bits** | Address --+ The 1 bit width register example I provided looks like: |<-- Register Bit Width (1) -->|<-- Register Bit Offset (31) -->| |<------------------ Access Size (32)-------------------------->| ^ | Address --+ Gary -- Gary Hade System x Enablement IBM Linux Technology Center 503-578-4503 IBM T/L: 775-4503 garyhade@xxxxxxxxxx http://www.ibm.com/linux/ltc -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html