From: Joel Holdsworth <joel@airwebreathe.org.uk>
To: Marek Vasut <marex@denx.de>,
atull@opensource.altera.com, moritz.fischer@ettus.com,
geert@linux-m68k.org, robh@kernel.org,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-spi@vger.kernel.org, clifford@clifford.at
Subject: Re: [PATCH v8 3/3] fpga: Add support for Lattice iCE40 FPGAs
Date: Tue, 8 Nov 2016 10:13:58 -0700 [thread overview]
Message-ID: <a86d41da-c7df-4c07-d18e-b751cff9edc7@airwebreathe.org.uk> (raw)
In-Reply-To: <4bdba358-db18-48f1-3286-a7a7f4c30215@denx.de>
Hi Marek,
>>> Should be this way for the sake of readability, fix globally:
>>>
>>> struct spi_transfer assert_cs_then_reset_delay = {
>>> .cs_change = 1,
>>> .delay_usecs = ICE40_SPI_FPGAMGR_RESET_DELAY
>>> };
>>
>> Sure ok. Personally, I prefer it to be concise, but I'm happy to accept
>> the norms.
>
> I prefer it to be readable :)
>
I'll conform to what you're saying.
But I just want to point out that this...
spi_message_add_tail(&(struct spi_transfer){.cs_change = 1,
.delay_usecs = ICE40_SPI_FPGAMGR_RESET_DELAY}, &message);
...is clearly more readable than this...
struct spi_transfer assert_cs_then_reset_delay = {
.cs_change = 1,
.delay_usecs = ICE40_SPI_FPGAMGR_RESET_DELAY
};
....
<30 lines of unrelated code>
....
spi_message_add_tail(&assert_cs_then_reset_delay, &message);
...in my opinion anyway ;)
>> Previously I had a copy of spi_set_cs copy-pasted into my driver, but in
>> the end I decided to replace that with the zero-length transfers because
>> there's a danger that if the original spi_set_cs() gets rewritten some
>> time, my copy-paste code would leave around some nasty legacy.
>>
>> On the whole, I don't think the zero-length transfers are too
>> egregiously bad, and all the alternatives seem worse to me.
>
> So why not turn the CS line into GPIO and just toggle the GPIO?
>
Two reasons.
1. On some devices the CS line is built into the SPI master, rather than
being a normal GPIO.
2. The SPI driver stack addresses SPI devices in terms of which CS line
they are attached to. You can't have an spi_device in the kernel where
the SPI driver machinery doesn't have a CS line to control. Moreover it
needs to be possible for another SPI device to interrupt a running
transfer to the FPGA. Supporting this involves the SPI framework
managing the CS line.
Thanks
Joel
next prev parent reply other threads:[~2016-11-08 17:14 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-07 2:49 [PATCH v8 1/3] of: Add vendor prefix for Lattice Semiconductor Joel Holdsworth
2016-11-07 2:49 ` [PATCH v8 2/3] Documentation: Add binding document for Lattice iCE40 FPGA manager Joel Holdsworth
2016-11-07 17:53 ` Marek Vasut
2016-11-07 18:57 ` Joel Holdsworth
2016-11-14 16:11 ` Rob Herring
2016-11-18 18:56 ` atull
2016-11-18 19:17 ` Moritz Fischer
2016-11-18 19:28 ` Marek Vasut
2016-11-07 2:49 ` [PATCH v8 3/3] fpga: Add support for Lattice iCE40 FPGAs Joel Holdsworth
2016-11-07 18:01 ` Marek Vasut
2016-11-07 18:49 ` Joel Holdsworth
2016-11-07 18:53 ` Marek Vasut
2016-11-08 17:06 ` Moritz Fischer
2016-11-08 17:30 ` Joel Holdsworth
2016-11-09 12:01 ` Marek Vasut
2016-11-09 18:37 ` Joel Holdsworth
2016-11-09 18:39 ` Marek Vasut
2016-11-09 18:54 ` Joel Holdsworth
2016-11-10 12:11 ` Marek Vasut
2016-11-08 17:13 ` Joel Holdsworth [this message]
2016-11-07 18:26 ` Moritz Fischer
2016-11-07 19:02 ` Joel Holdsworth
2016-11-07 21:41 ` Moritz Fischer
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=a86d41da-c7df-4c07-d18e-b751cff9edc7@airwebreathe.org.uk \
--to=joel@airwebreathe.org.uk \
--cc=atull@opensource.altera.com \
--cc=clifford@clifford.at \
--cc=devicetree@vger.kernel.org \
--cc=geert@linux-m68k.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-spi@vger.kernel.org \
--cc=marex@denx.de \
--cc=moritz.fischer@ettus.com \
--cc=robh@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).