Messages in this thread |  | | Subject | Re: [PATCH] spi: Add FSI-attached SPI controller driver | From | Eddie James <> | Date | Fri, 7 Feb 2020 14:04:22 -0600 |
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On 2/7/20 1:39 PM, Andy Shevchenko wrote: > On Fri, Feb 7, 2020 at 9:28 PM Eddie James <eajames@linux.vnet.ibm.com> wrote: >> On 2/5/20 9:51 AM, Andy Shevchenko wrote: >>> On Tue, Feb 4, 2020 at 6:06 PM Eddie James <eajames@linux.ibm.com> wrote: >>>> On 2/4/20 5:02 AM, Andy Shevchenko wrote: >>>>> On Mon, Feb 3, 2020 at 10:33 PM Eddie James <eajames@linux.vnet.ibm.com> wrote: >>>>>> On 1/30/20 10:37 AM, Andy Shevchenko wrote: > ... > >>>>>>>> + for (i = 0; i < num_bytes; ++i) >>>>>>>> + rx[i] = (u8)((in >> (8 * ((num_bytes - 1) - i))) & 0xffULL); >>>>>>> Redundant & 0xffULL part. >>>>>>> >>>>>>> Isn't it NIH of get_unalinged_be64 / le64 or something similar? >>>>>> No, these are shift in/out operations. The read register will also have >>>>>> previous operations data in them and must be extracted with only the >>>>>> correct number of bytes. >>>>> Why not to call put_unaligned() how the tail in this case (it's 0 or >>>>> can be easily made to be 0) will affect the result? >>>> The shift-in is not the same as any byte-swap or unaligned operation. >>>> For however many bytes we've read, we start at that many bytes >>>> left-shifted in the register and copy out to our buffer, moving right >>>> for each next byte... I don't think there is an existing function for >>>> this operation. >>> For me it looks like >>> >>> u8 tmp[8]; >>> >>> put_unaligned_be64(in, tmp); >>> memcpy(rx, tmp, num_bytes); >>> >>> put_unaligned*() is just a method to unroll the value to the u8 buffer. >>> See, for example, linux/unaligned/be_byteshift.h implementation. >> >> Unforunately it is not the same. put_unaligned_be64 will take the >> highest 8 bits (0xff00000000000000) and move it into tmp[0]. Then >> 0x00ff000000000000 into tmp[1], etc. This is only correct for this >> driver IF my transfer is 8 bytes. If, for example, I transfer 5 bytes, >> then I need 0x000000ff00000000 into tmp[0], 0x00000000ff000000 into >> tmp[1], etc. So I think my current implementation is correct. > Yes, I missed correction of the start address in memcpy(). Otherwise > it's still the same what I was talking about.
I see now, yes, thanks.
Do you think this is worth a v3? Perhaps put_unaligned is slightly more optimized than the loop but there is more memory copy with that way too.
Eddie
> >>>>>>>> + return num_bytes; >>>>>>>> +} >>>>>>>> +static int fsi_spi_data_out(u64 *out, const u8 *tx, int len) >>>>>>>> +{ >>>>>>> Ditto as for above function. (put_unaligned ...) >>>>> Ditto. >>>> I don't understand how this could work for transfers of less than 8 >>>> bytes, any put_unaligned would access memory that it doesn't own. >>> Ditto. >>> >>>>>>>> +}
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