All of lore.kernel.org
 help / color / mirror / Atom feed
From: Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
To: Chris Ruehl <chris.ruehl-CR359r9tUDPXPF5Rlphj1Q@public.gmane.org>
Cc: linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org,
	anton.bondarenko.sama-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
	festevam-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
	kernel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org
Subject: Re: [PATCH] spi-imx: imx6q add single burst transfer support
Date: Wed, 1 Jun 2016 08:54:37 +0200	[thread overview]
Message-ID: <20160601065437.GI31666@pengutronix.de> (raw)
In-Reply-To: <1464756628-25463-1-git-send-email-chris.ruehl-CR359r9tUDPXPF5Rlphj1Q@public.gmane.org>

On Wed, Jun 01, 2016 at 12:50:28PM +0800, Chris Ruehl wrote:
> The patch add support for single burst transfer where chipselect will
> hold active until transfer completes with a limit to 2^7 words transferred.
> The single-burst-mode need set the burstlength in ECSPI_CONREG.BURST_LENGTH
> and clear the ecspi channel related ss_ctl flag in ECSPI_CONFIGREG.SS_CTL.
> 
> The single-burst-mode is disabled by default. The activation from spidev
> is implemented by set bit0 of the xfer.speed_hz, which don't break anything
> in the mx51_ecspi_clkdiv() function.
> 
> xfer[0].speed_hz = 2000000 | 0x1; /* enable single burst mode with 1hz */

Erm, no. This is not acceptable in many ways. First of all the SPI API
between the kernel and userspace is driver agnostic. There is simply no
place for passing driver specific quirks from userspace to the spi-imx
driver. Then there is no API change needed because the way SPI
messages should be translated to the wire is well defined, the spi-imx
driver is just doing it wrong in this case which might be worth fixing.
This could be done without passing a "do it right" flag to the driver.

As noted in my response to the previous patch, I don't think we need a
fix for this at all, because we can always use GPIO chip selects which
works reliably not only in this case, but also in other cases where the
controller driven chipselect falls apart.

IMO there is only a single reason to keep controller driven chip select
support at all: On i.MX31 there is one dedicated chip select which can't
be configured as GPIO.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |
--
To unsubscribe from this list: send the line "unsubscribe linux-spi" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

  parent reply	other threads:[~2016-06-01  6:54 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-01  4:50 Chris Ruehl
     [not found] ` <1464756628-25463-1-git-send-email-chris.ruehl-CR359r9tUDPXPF5Rlphj1Q@public.gmane.org>
2016-06-01  5:06   ` Chris Ruehl
2016-06-01  6:54   ` Sascha Hauer [this message]
     [not found]     ` <20160601065437.GI31666-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
2016-06-01  7:09       ` Chris Ruehl
     [not found]         ` <574E8A19.3020603-CR359r9tUDPXPF5Rlphj1Q@public.gmane.org>
2016-06-01 14:32           ` Mark Brown
     [not found]             ` <20160601143213.GA2282-GFdadSzt00ze9xe1eoZjHA@public.gmane.org>
2016-06-02  1:27               ` Chris Ruehl

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=20160601065437.GI31666@pengutronix.de \
    --to=s.hauer-bicnvbalz9megne8c9+irq@public.gmane.org \
    --cc=anton.bondarenko.sama-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org \
    --cc=broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org \
    --cc=chris.ruehl-CR359r9tUDPXPF5Rlphj1Q@public.gmane.org \
    --cc=festevam-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org \
    --cc=kernel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org \
    --cc=linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
    --subject='Re: [PATCH] spi-imx: imx6q add single burst transfer support' \
    /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

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.