All of lore.kernel.org
 help / color / mirror / Atom feed
From: Heiko Stuebner <heiko@sntech.de>
To: Stephen Boyd <sboyd@codeaurora.org>
Cc: mturquette@baylibre.com, linux-clk@vger.kernel.org,
	linux-rockchip@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	James Hogan <james.hogan@imgtec.com>,
	Zhang Qing <zhangqing@rock-chips.com>,
	Joonyoung Shim <jy0922.shim@samsung.com>
Subject: Re: [PATCH v2] clk-divider: make sure read-only dividers do not write to their register
Date: Wed, 20 Jan 2016 23:29:56 +0100	[thread overview]
Message-ID: <2694181.qDMgtzpC9k@phil> (raw)
In-Reply-To: <20160120221604.GC12841@codeaurora.org>

Am Mittwoch, 20. Januar 2016, 14:16:56 schrieb Stephen Boyd:
> On 01/20, Heiko Stuebner wrote:
> > Commit e6d5e7d90be9 ("clk-divider: Fix READ_ONLY when divider > 1")
> > removed the special ops struct for read-only clocks and instead opted
> > to handle them regularly.
> > 
> > On the rk3368 this results in breakage as aclkm now gets set a value.
> > While it is the same divider value, the A53 core still doesn't like it,
> > which can result in the cpu ending up in a hang.
> > The reason being that "ACLKENMasserts one clock cycle before the rising
> > edge of ACLKM" and the clock should only be touched when STANDBYWFIL2
> > is asserted.
> > 
> > So make sure read-only clocks don't touch the clock-register at all
> > even if only writing the same value, as even writing the same value
> > may not be safe in all cases.
> > 
> > Fixes: e6d5e7d90be9 ("clk-divider: Fix READ_ONLY when divider > 1")
> > Reported-by: Zhang Qing <zhangqing@rock-chips.com>
> > Signed-off-by: Heiko Stuebner <heiko@sntech.de>
> > Reviewed-by: James Hogan <james.hogan@imgtec.com>
> > ---
> 
> Hmph, the same patch[1] has been sitting in my inbox for months
> now but I never got a response to my last question and then
> forgot about it. I'll repeat the question here and hopefully we
> can finish the discussion.
> 
> Maybe it would make more sense to have different ops for read
> only dividers? The clk_set_rate op would be empty, while we would
> have proper recalc_rate and round_rate ops. We can't just flat
> out revert commit e6d5e7d90be9 (clk-divider: Fix READ_ONLY when
> divider > 1, 2014-11-14) because that will introduce the problem
> that it was fixing, but as long as we implement round_rate in
> addition to recalc_rate it should work.
> 
> [1]
> http://lkml.kernel.org/r/1428392806-14538-1-git-send-email-jy0922.shim@sa
> msung.com

Sorry for the second submission then. That really is from quite a while ago. 
Reintroducing a secondary ops-struct with a round-rate sounds fine for my 
side - I'll give that a shot tomorrow.


Heiko

WARNING: multiple messages have this Message-ID (diff)
From: heiko@sntech.de (Heiko Stuebner)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] clk-divider: make sure read-only dividers do not write to their register
Date: Wed, 20 Jan 2016 23:29:56 +0100	[thread overview]
Message-ID: <2694181.qDMgtzpC9k@phil> (raw)
In-Reply-To: <20160120221604.GC12841@codeaurora.org>

Am Mittwoch, 20. Januar 2016, 14:16:56 schrieb Stephen Boyd:
> On 01/20, Heiko Stuebner wrote:
> > Commit e6d5e7d90be9 ("clk-divider: Fix READ_ONLY when divider > 1")
> > removed the special ops struct for read-only clocks and instead opted
> > to handle them regularly.
> > 
> > On the rk3368 this results in breakage as aclkm now gets set a value.
> > While it is the same divider value, the A53 core still doesn't like it,
> > which can result in the cpu ending up in a hang.
> > The reason being that "ACLKENMasserts one clock cycle before the rising
> > edge of ACLKM" and the clock should only be touched when STANDBYWFIL2
> > is asserted.
> > 
> > So make sure read-only clocks don't touch the clock-register at all
> > even if only writing the same value, as even writing the same value
> > may not be safe in all cases.
> > 
> > Fixes: e6d5e7d90be9 ("clk-divider: Fix READ_ONLY when divider > 1")
> > Reported-by: Zhang Qing <zhangqing@rock-chips.com>
> > Signed-off-by: Heiko Stuebner <heiko@sntech.de>
> > Reviewed-by: James Hogan <james.hogan@imgtec.com>
> > ---
> 
> Hmph, the same patch[1] has been sitting in my inbox for months
> now but I never got a response to my last question and then
> forgot about it. I'll repeat the question here and hopefully we
> can finish the discussion.
> 
> Maybe it would make more sense to have different ops for read
> only dividers? The clk_set_rate op would be empty, while we would
> have proper recalc_rate and round_rate ops. We can't just flat
> out revert commit e6d5e7d90be9 (clk-divider: Fix READ_ONLY when
> divider > 1, 2014-11-14) because that will introduce the problem
> that it was fixing, but as long as we implement round_rate in
> addition to recalc_rate it should work.
> 
> [1]
> http://lkml.kernel.org/r/1428392806-14538-1-git-send-email-jy0922.shim at sa
> msung.com

Sorry for the second submission then. That really is from quite a while ago. 
Reintroducing a secondary ops-struct with a round-rate sounds fine for my 
side - I'll give that a shot tomorrow.


Heiko

  reply	other threads:[~2016-01-20 22:29 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-20 14:42 [PATCH] clk-divider: make sure read-only dividers do not write to their register Heiko Stuebner
2016-01-20 14:42 ` Heiko Stuebner
2016-01-20 14:57 ` James Hogan
2016-01-20 14:57   ` James Hogan
2016-01-20 14:57   ` James Hogan
2016-01-20 19:51 ` [PATCH v2] " Heiko Stuebner
2016-01-20 19:51   ` Heiko Stuebner
2016-01-20 19:51   ` Heiko Stuebner
2016-01-20 22:16   ` Stephen Boyd
2016-01-20 22:16     ` Stephen Boyd
2016-01-20 22:29     ` Heiko Stuebner [this message]
2016-01-20 22:29       ` Heiko Stuebner

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=2694181.qDMgtzpC9k@phil \
    --to=heiko@sntech.de \
    --cc=james.hogan@imgtec.com \
    --cc=jy0922.shim@samsung.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-clk@vger.kernel.org \
    --cc=linux-rockchip@lists.infradead.org \
    --cc=mturquette@baylibre.com \
    --cc=sboyd@codeaurora.org \
    --cc=zhangqing@rock-chips.com \
    /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 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.