From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Eddie James <eajames@linux.vnet.ibm.com>
Cc: Eddie James <eajames@linux.ibm.com>,
linux-spi <linux-spi@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Mark Brown <broonie@kernel.org>, Joel Stanley <joel@jms.id.au>,
Andrew Jeffery <andrew@aj.id.au>
Subject: Re: [PATCH] spi: Add FSI-attached SPI controller driver
Date: Fri, 7 Feb 2020 22:34:17 +0200 [thread overview]
Message-ID: <CAHp75VdO2+Kkgo1Nv3EJXTMqP6Y7XgLVXtRvURk6Zz0p=R9zNQ@mail.gmail.com> (raw)
In-Reply-To: <cd8a7279-beb2-39e6-58e6-6ea505665547@linux.vnet.ibm.com>
On Fri, Feb 7, 2020 at 10:04 PM Eddie James <eajames@linux.vnet.ibm.com> wrote:
> 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.
> >>> 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.
I already forgot the entire context when this has been called. Can you
summarize what the sequence(s) of num_bytes are expected usually.
IIUC if packets small, less than 8 bytes, than num_bytes will be that value.
Otherwise it will be something like 8 + 8 + 8 ... + tail. Is it
correct assumption?
> >>>>>>>> + return num_bytes;
> >>>>>>>> +}
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2020-02-07 20:34 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-29 20:08 [PATCH] spi: Add FSI-attached SPI controller driver Eddie James
2020-01-30 14:46 ` Mark Brown
2020-01-30 15:32 ` Eddie James
2020-01-30 16:37 ` Andy Shevchenko
2020-02-03 20:33 ` Eddie James
2020-02-04 11:02 ` Andy Shevchenko
2020-02-04 16:06 ` Eddie James
2020-02-05 15:51 ` Andy Shevchenko
2020-02-07 19:28 ` Eddie James
2020-02-07 19:39 ` Andy Shevchenko
2020-02-07 20:04 ` Eddie James
2020-02-07 20:34 ` Andy Shevchenko [this message]
2020-02-07 20:59 ` Eddie James
2020-02-07 22:04 ` Andy Shevchenko
2020-02-10 20:05 ` Eddie James
2020-02-10 20:33 ` Andy Shevchenko
2020-02-10 20:50 ` Eddie James
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