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From: Andy Shevchenko <andy.shevchenko-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: Eddie James <eajames-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>
Cc: Eddie James
	<eajames-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>,
	linux-spi <linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Linux Kernel Mailing List
	<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Joel Stanley <joel-U3u1mxZcP9KHXe+LvDLADg@public.gmane.org>,
	Andrew Jeffery <andrew-zrmu5oMJ5Fs@public.gmane.org>
Subject: Re: [PATCH] spi: Add FSI-attached SPI controller driver
Date: Wed, 5 Feb 2020 17:51:52 +0200	[thread overview]
Message-ID: <CAHp75VfOM5Rd3LRBtvyT96G=+J4KxTRoSVUcQTj+RxrGyZMMnQ@mail.gmail.com> (raw)
In-Reply-To: <744f0019-8656-eec1-cb9a-7e70cd042587-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>

On Tue, Feb 4, 2020 at 6:06 PM Eddie James <eajames-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org> wrote:
> On 2/4/20 5:02 AM, Andy Shevchenko wrote:
> > On Mon, Feb 3, 2020 at 10:33 PM Eddie James <eajames-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org> wrote:
> >> On 1/30/20 10:37 AM, Andy Shevchenko wrote:
> >>> On Wed, Jan 29, 2020 at 10:09 PM Eddie James <eajames-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org> wrote:

...

> >>>> +       struct device *dev;
> >>> Isn't fsl->dev the same?
> >>> Perhaps kernel doc to explain the difference?
> >>
> >> No, it's not the same, as dev here is the SPI controller. I'll add a
> >> comment.
> > Why to have duplication then?
>
>
> Nothing is being duplicated, the two variables are storing entirely
> different information, both of which are necessary for each SPI
> controller that this driver is driving.

Oh, I see now, thanks!

...

> >>>> +       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.

> >>>> +       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.

> >>>> +}

-- 
With Best Regards,
Andy Shevchenko

  parent reply	other threads:[~2020-02-05 15:51 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
     [not found] ` <1580328504-436-1-git-send-email-eajames-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>
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
     [not found]       ` <29f6cc86-69ca-bc88-b6ae-2b1a24c0dae3-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2020-02-04 11:02         ` Andy Shevchenko
     [not found]           ` <CAHp75Vf3NCkbw39E+d_nf+AyViG2o-u5HxrCjXXmbGk4LaFLog-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-02-04 16:06             ` Eddie James
     [not found]               ` <744f0019-8656-eec1-cb9a-7e70cd042587-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>
2020-02-05 15:51                 ` Andy Shevchenko [this message]
     [not found]                   ` <CAHp75VfOM5Rd3LRBtvyT96G=+J4KxTRoSVUcQTj+RxrGyZMMnQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-02-07 19:28                     ` Eddie James
     [not found]                       ` <90973143-bd0a-33cf-9eb8-a83be1a9b415-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2020-02-07 19:39                         ` Andy Shevchenko
     [not found]                           ` <CAHp75Vf6HJw=SpK9_HUgcMaaabs5pZEybP4SS-gc1wz5GRcqeg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-02-07 20:04                             ` Eddie James
     [not found]                               ` <cd8a7279-beb2-39e6-58e6-6ea505665547-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2020-02-07 20:34                                 ` Andy Shevchenko
     [not found]                                   ` <CAHp75VdO2+Kkgo1Nv3EJXTMqP6Y7XgLVXtRvURk6Zz0p=R9zNQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-02-07 20:59                                     ` Eddie James
     [not found]                                       ` <ca8a832e-ceeb-3ce1-9807-96ee41e0f166-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2020-02-07 22:04                                         ` Andy Shevchenko
     [not found]                                           ` <CAHp75VduJn=kMuriGNAGk1ZrL4b2LpqEn5c8AC=PHFKrgoz=vg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-02-10 20:05                                             ` Eddie James
2020-02-10 20:33                                               ` Andy Shevchenko
     [not found]                                                 ` <CAHp75VfpRV7UDMpPKo8Vu1PaOfLjUG24yUdkg8ip9=923cwarA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-02-10 20:50                                                   ` Eddie James

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