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From: Colin Cross <ccross@android.com>
To: Stephen Boyd <sboyd@codeaurora.org>
Cc: linux-tegra@vger.kernel.org,
	Russell King <linux@arm.linux.org.uk>,
	konkers@android.com, linux-kernel@vger.kernel.org,
	olof@lixom.net, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 12/21] ARM: tegra: clock: Add shared bus clock type
Date: Wed, 16 Feb 2011 13:01:09 -0800	[thread overview]
Message-ID: <AANLkTi=knKY65xaOT85jFidy6Be8K8RT0L1XtGqq_v2V@mail.gmail.com> (raw)
In-Reply-To: <4D5C34E0.5000209@codeaurora.org>

On Wed, Feb 16, 2011 at 12:34 PM, Stephen Boyd <sboyd@codeaurora.org> wrote:
> On 02/13/2011 01:40 AM, Colin Cross wrote:
>> +/* shared bus ops */
>> +/*
>> + * Some clocks may have multiple downstream users that need to request a
>> + * higher clock rate.  Shared bus clocks provide a unique shared_bus_user
>> + * clock to each user.  The frequency of the bus is set to the highest
>> + * enabled shared_bus_user clock, with a minimum value set by the
>> + * shared bus.
>> + */
>> +static void tegra_clk_shared_bus_update(struct clk *bus)
>> +{
>> +     struct clk *c;
>> +     unsigned long rate = bus->min_rate;
>> +
>> +     list_for_each_entry(c, &bus->shared_bus_list, u.shared_bus_user.node)
>> +             if (c->u.shared_bus_user.enabled)
>> +                     rate = max(c->u.shared_bus_user.rate, rate);
>> +
>> +     if (rate != clk_get_rate(bus))
>> +             clk_set_rate(bus, rate);
>
> What do you do if clk_set_rate() fails? Should you unwind all the state
> such as the rate and if it's enabled/disabled? Or is it safe to say
> clk_set_rate() can't fail unless the kernel is buggy in which case why
> aren't all those return -E* in the set rate functions just BUG_ONs?

In general, clk_set_rate can fail and return an error, but in this
case the failure may not be directly related to the driver that called
into tegra_clk_shared_bus_update.  For example, if clk_disable is
called on a shared clock handle, the rate may drop to the rate
requested by another shared clock handle.  clk_disable cannot fail, so
there's nothing that could be done with the return code, and the
problem was not caused by the driver that called clk_disable, so an
error would be meaningless.

I will modify tegra_clk_shared_bus_update to BUG on a failed
clk_set_rate, and modify tegra_clk_shared_bus_set_rate to
call clk_round_rate on the parent to ensure that the requested rate is valid.

>> +};
>> +
>> +static void tegra_clk_shared_bus_init(struct clk *c)
>> +{
>> +     c->max_rate = c->parent->max_rate;
>> +     c->u.shared_bus_user.rate = c->parent->max_rate;
>> +     c->state = OFF;
>> +#ifdef CONFIG_DEBUG_FS
>> +     c->set = 1;
>> +#endif
>> +
>> +     list_add_tail(&c->u.shared_bus_user.node,
>> +             &c->parent->shared_bus_list);
>> +}
>> +
>> +static int tegra_clk_shared_bus_set_rate(struct clk *c, unsigned long rate)
>> +{
>> +     c->u.shared_bus_user.rate = rate;
>> +     tegra_clk_shared_bus_update(c->parent);
>> +     return 0;
>> +}
>> +
>> +static long tegra_clk_shared_bus_round_rate(struct clk *c, unsigned long rate)
>> +{
>> +     return clk_round_rate(c->parent, rate);
>> +}
>> +
>> +static int tegra_clk_shared_bus_enable(struct clk *c)
>> +{
>> +     c->u.shared_bus_user.enabled = true;
>> +     tegra_clk_shared_bus_update(c->parent);
>> +     return 0;
>> +}
>
> Shouldn't you call clk_enable(c->parent)? And do you need to check for
> errors from clk_enable()?

clk_enable on the parent is handled by the clock op implementation in
mach-tegra/clock.c

>> +
>> +static void tegra_clk_shared_bus_disable(struct clk *c)
>> +{
>> +     c->u.shared_bus_user.enabled = false;
>> +     tegra_clk_shared_bus_update(c->parent);
>> +}
>
> And a similar clk_disable(c->parent) here.

Same for disable

  reply	other threads:[~2011-02-16 21:01 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1297590033-15035-1-git-send-email-ccross@android.com>
2011-02-13  9:40 ` [PATCH 01/21] ARM: tegra: clock: enable clk reset for non-peripheral clocks Colin Cross
2011-02-13  9:40 ` [PATCH 02/21] ARM: tegra: clock: Don't BUG on changing an enabled PLL Colin Cross
2011-02-13  9:40 ` [PATCH 03/21] ARM: tegra: clock: Drop debugging Colin Cross
2011-02-13  9:40 ` [PATCH 04/21] ARM: tegra: clock: Don't use PLL lock bits Colin Cross
2011-02-13  9:40 ` [PATCH 05/21] ARM: tegra: clock: Disable clocks left on by bootloader Colin Cross
2011-02-13  9:40 ` [PATCH 06/21] ARM: tegra: clock: Initialize clocks that have no enable Colin Cross
2011-02-13  9:40 ` [PATCH 07/21] ARM: tegra: clock: Drop CPU dvfs Colin Cross
2011-02-13  9:40 ` [PATCH 08/21] ARM: tegra: clock: Rearrange static clock tables Colin Cross
2011-02-13  9:40 ` [PATCH 09/21] ARM: tegra: clock: Move unshared clk struct members into union Colin Cross
2011-02-13  9:40 ` [PATCH 10/21] ARM: tegra: clock: Convert global lock to a lock per clock Colin Cross
2011-02-13  9:40 ` [PATCH 11/21] ARM: tegra: cpufreq: Take an extra reference to pllx Colin Cross
2011-02-13  9:40 ` [PATCH 12/21] ARM: tegra: clock: Add shared bus clock type Colin Cross
2011-02-16 20:34   ` Stephen Boyd
2011-02-16 21:01     ` Colin Cross [this message]
2011-02-16 21:51       ` Stephen Boyd
2011-02-16 22:03         ` Colin Cross
2011-02-13  9:40 ` [PATCH 13/21] ARM: tegra: clock: Remove unnecessary uses of #ifdef CONFIG_DEBUG_FS Colin Cross
2011-02-13  9:40 ` [PATCH 14/21] ARM: tegra: clock: Refcount periph clock enables Colin Cross
2011-02-13  9:40 ` [PATCH 15/21] ARM: tegra: clock: Round rate before setting rate Colin Cross
2011-02-13  9:40 ` [PATCH 16/21] ARM: tegra: Add external memory controller driver Colin Cross
2011-02-13  9:40 ` [PATCH 17/21] ARM: tegra: clocks: Add emc scaling Colin Cross
2011-02-13  9:40 ` [PATCH 18/21] ARM: tegra: cpufreq: Adjust memory frequency with cpu frequency Colin Cross
2011-02-13  9:40 ` [PATCH 19/21] ARM: tegra: clock: Add function to set SDMMC tap delay Colin Cross
2011-02-13  9:40 ` [PATCH 20/21] ARM: tegra: clock: Fix clock issues in suspend Colin Cross
2011-02-13  9:40 ` [PATCH 21/21] ARM: tegra: clock: Miscellaneous clock updates Colin Cross

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