Re: [Qemu-devel] [PATCH arm-devs v1 11/15] xilinx_spips: Fix striping behaviour

[Peter Crosthwaite]

Hi Peter,

On Sat, Apr 6, 2013 at 4:59 AM, Peter Maydell <address@hidden> wrote:
> On 3 April 2013 05:33, Peter Crosthwaite <address@hidden> wrote:
>> The QSPI controller was using byte-wide stripes when striping across
>> the two flashes in dual parallel mode. The real hardware however uses
>> individual bit striping. QEMU misbehaves in the (corner) case where
>> data is written/read in dual-parallel mode and read/written back in
>> single mode.
>>
>> Signed-off-by: Peter Crosthwaite <address@hidden>
>> ---
>>
>>  hw/xilinx_spips.c |   74 
>> ++++++++++++++++++++++++++++++++++++++---------------
>>  1 files changed, 53 insertions(+), 21 deletions(-)
>>
>> diff --git a/hw/xilinx_spips.c b/hw/xilinx_spips.c
>> index a2019e4..43ce2d8 100644
>> --- a/hw/xilinx_spips.c
>> +++ b/hw/xilinx_spips.c
>> @@ -258,35 +258,67 @@ static void xilinx_spips_reset(DeviceState *d)
>>      xilinx_spips_update_cs_lines(s);
>>  }
>>
>> +static inline void stripe8(uint8_t *x, int num, bool dir)
>> +{
>> +    uint8_t r[num];
>> +    memset(r, 0, sizeof(uint8_t) * num);
>
> Don't interleave code and variable definitions, please.
>
>> +    int idx[2] = {0, 0};
>> +    int bit[2] = {0, 0};
>> +    int d = dir;
>> +
>> +    for (idx[0] = 0; idx[0] < num; ++idx[0]) {
>> +        for (bit[0] = 0; bit[0] < 8; ++bit[0]) {
>> +            r[idx[d]] |= x[idx[!d]] & 1 << bit[!d] ? 1 << bit[d] : 0;
>> +            idx[1] = (idx[1] + 1) % num;
>> +            if (!idx[1]) {
>> +                bit[1]++;
>> +            }
>> +        }
>> +    }
>> +    memcpy(x, r, sizeof(uint8_t) * num);
>> +}
>
> This function could really use a comment saying what it's doing...
>

+/* N way (num) in place bit striper. Lay out row wise bits (LSB to MSB)
+ * column wise (from element 0 to N-1). num is the length of x, and dir
+ * reverses the direction of the transform. Best illustrated by example:
+ * Each digit in the below array is a single bit (num == 3):
+ *
+ * {{ 76543210, }  ----- stripe (dir == false) -----> {{ FCheb630, }
+ *  { hgfedcba, }                                      { GDAfc741, }
+ *  { HGFEDCBA, }} <---- upstripe (dir == true) -----  { HEBgda52, }}
+ */
+

Regards,
Peter

>
> thanks
> -- PMM
>