About t1042 fsl sata driver

[Simon Glass]

Hi,

On Thu, 24 Dec 2020 at 03:47, Yusuf Kaya <ysf.kya34 at gmail.com> wrote:
>
> Hi,
>
> I'm confused about usage of DCC(Data DWord Count) Field of PRD Entries in fsl_sata.c
>
> In T1042 Reference manual, DCC field is explained as the following way;
>
> Data DWord count. A 0-based value that Indicates the length, in DWords, of the data block. A
> maximum length of 32 Mbytes may exist for any entry. Bits 1-0 of this field must always be 0 to
> indicate that size is in 4-byte words. A value of 24'b0 indicates a full 32 Mbytes transfer.
>
> but in the fsl driver code of u-boot, this field is acted like DBC(Data Byte Count). The following is part of the driver code that handles PRD Entries
>
>
> if (len < PRD_ENTRY_MAX_XFER_SZ) {
> ext_c_ddc = PRD_ENTRY_DATA_SNOOP | len;
> debug("ext_c_ddc1 = %08x, len = %08x\n\r", ext_c_ddc, len);
> prde->ext_c_ddc = cpu_to_le32(ext_c_ddc);
> prde_count++;
> prde++;
> break;
> } else {
> ext_c_ddc = PRD_ENTRY_DATA_SNOOP; /* 4M bytes */
> debug("ext_c_ddc2 = %08x, len = %08x\n\r", ext_c_ddc, len);
> prde->ext_c_ddc = cpu_to_le32(ext_c_ddc);
> buffer += PRD_ENTRY_MAX_XFER_SZ;
> len -= PRD_ENTRY_MAX_XFER_SZ;
> prde_count++;
> prde++;
> }
>
>
> In the above code, PRD_ENTRY_MAX_XFER_SZ is defined as 4 MB and DDC
> field of PDR entries are using like DBC. I didnt understand that part of
> the code and Reference Manual also specifies maximum transfer size of
> data is 32 Mbytes not 4Mbytes.
>
>
> the fsl sata driver code of u-boot is working but according to t1042 reference manual it should work wrongly.
>
>
> I guess I misunderstand something about PRD Entries. Could you explain it for me ?

I assume this is fsl_sata.c so:

+Peng Fan

Regards,
Simon