[PATCH/RFC 0/4] sh-sci : Do not derive regshift from regsize

From: Geert Uytterhoeven <geert+renesas@glider.be>
To: Chris Brandt <chris.brandt@renesas.com>,
	Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>,
	Ulrich Hecht <uli@fpond.eu>,
	Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	linux-renesas-soc@vger.kernel.org, linux-sh@vger.kernel.org,
	linux-serial@vger.kernel.org,
	Geert Uytterhoeven <geert+renesas@glider.be>
Subject: [PATCH/RFC 0/4] sh-sci : Do not derive regshift from regsize
Date: Mon, 06 Aug 2018 14:07:51 +0000	[thread overview]
Message-ID: <20180806140755.24087-1-geert+renesas@glider.be> (raw)

	Hi all,

This RFC patch series was sparked by noticing that commit 2d4dd0da45401c7a
("serial: sh-sci: Allow for compressed SCIF address") broke earlycon
support on most Renesas ARM SoCs using SCIF ports, and by the fragility of
deriving regshift from the register block size (which may be rounded up):
  1. The first patch is an old patch from Sato-san, which I never really
     understood.  But it turned out to be a dependency for patch 2.
  2. Patch 2 makes sure regshift is initialized when using earlycon,
     unbreaking the serial console on e.g. R-Car Gen2 and Gen3.
  3. Patch 3 reverts the patch that started deriving regshift from the
     register block size, and that removed the plat_sci_port.regshift
     field.  Which is a field I needed again in patch 4.
  4. Patch 4 removes the remaining regshift derivations on DT platforms.
 (5. I didn't bother writing patch 5, which involves adding .regshift
     initializations to all SH board files that need it.)

However, I'm not happy with the end result, so please DO NOT apply this!
As I spent almost a full day on this, and would still like to know the
story about "sh-sci: Use a separate sci_port for earlycon", I decided to
post it anyway.

As earlycon will be broken in v4.19-rc1 on RZ/A1, RZ/G, and R-Car, assuming
no other actions are taken, an alternative solution would be to:
  1. Revert commit 7acece71a517cad8 ("serial: sh-sci: Remove
     SCIx_RZ_SCIFA_REGTYPE"),
  2. Revert commit 2d4dd0da45401c7a ("serial: sh-sci: Allow for compressed
     SCIF address") alternative,
  3. Add an OF_EARLYCON_DECLARE() for RZ/A2, to fix earlycon on RZ/A2.

What do you think?
Thanks for your comments!

P.S. Apparently SCIx_SH4_SCIF_REGTYPE and SCIx_SH2_SCIF_FIFODATA_REGTYPE
     are identical?

Geert Uytterhoeven (3):
  [RFC] sh-sci: Take into account regshift to fix earlycon breakage
  [RFC] Revert "serial: sh-sci: Compute the regshift value for SCI
    ports"
  [RFC] sh-sci: Derive regshift value from DT compatible value

Yoshinori Sato (1):
  [RFC] sh-sci: Use a separate sci_port for earlycon

 arch/sh/kernel/cpu/sh3/setup-sh770x.c |  1 +
 arch/sh/kernel/cpu/sh4/setup-sh7750.c |  3 +-
 arch/sh/kernel/cpu/sh4/setup-sh7760.c | 10 +---
 drivers/tty/serial/sh-sci.c           | 68 +++++++++++++++++----------
 include/linux/serial_sci.h            |  1 +
 5 files changed, 49 insertions(+), 34 deletions(-)

-- 
2.17.1

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds