From: maxime.coquelin@st•com (Maxime Coquelin)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/5] clocksource: st_lpc: Add LPC timer as a clocksource.
Date: Wed, 29 Apr 2015 17:48:11 +0200 [thread overview]
Message-ID: <5540FD3B.1040702@st.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1504211153580.13914@nanos>
Hello Thomas,
On 04/21/2015 11:56 AM, Thomas Gleixner wrote:
> On Fri, 17 Apr 2015, Peter Griffin wrote:
>> +/* Low Power Timer */
>> +#define LPC_LPT_LSB_OFF 0x400
>> +#define LPC_LPT_MSB_OFF 0x404
>> +#define LPC_LPT_START_OFF 0x408
>> +
>> +struct st_lpc {
>> + struct clk *clk;
>> + void __iomem *iomem_cs;
>> +};
>> +
>> +static struct st_lpc *st_lpc;
>> +
>> +static u64 notrace st_lpc_counter_read(void)
>> +{
>> + u64 counter;
>> + u32 lower;
>> + u32 upper, old_upper;
>> +
>> + upper = readl_relaxed(st_lpc->iomem_cs + LPC_LPT_MSB_OFF);
>> + do {
>> + old_upper = upper;
>> + lower = readl_relaxed(st_lpc->iomem_cs + LPC_LPT_LSB_OFF);
>> + upper = readl_relaxed(st_lpc->iomem_cs + LPC_LPT_MSB_OFF);
>> + } while (upper != old_upper);
>> +
>> + counter = upper;
>> + counter <<= 32;
>> + counter |= lower;
>> + return counter;
>
> What's the point of this exercise? The kernel can handle 32bit
> clocksources nicely. So why do you want to artificially expand them to
> 64bit by adding useless loops and hoops to a hotpath?
I agree we should use only the lower 32 bits.
This timer is moreover clocked at a slow rate (30MHz), so we won't have
too much interrupts.
Peter, doing that, you could use something like this directly:
clocksource_mmio_init(st_lpc->iomem_cs + LPC_LPT_LSB_OFF,
"st_lpc_timer", rate,
200, 24, clocksource_mmio_readl_down);
Thanks,
Maxime
>
> Thanks,
>
> tglx
next prev parent reply other threads:[~2015-04-29 15:48 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-17 10:50 [PATCH 0/5] Add st_lpc clocksource timer driver Peter Griffin
2015-04-17 10:50 ` [PATCH 1/5] clocksource: st_lpc: Add LPC timer as a clocksource Peter Griffin
2015-04-17 21:16 ` Paul Bolle
2015-04-20 7:14 ` Peter Griffin
2015-04-21 9:56 ` Thomas Gleixner
2015-04-29 15:48 ` Maxime Coquelin [this message]
2015-05-02 16:36 ` Peter Griffin
2015-04-17 10:50 ` [PATCH 2/5] clocksource: st_lpc: Add DT bindings documentation for lpc timer Peter Griffin
2015-04-17 10:50 ` [PATCH 3/5] MAINTAINERS: Add st_lpc.c to ARCH/STI section of maintainers Peter Griffin
2015-04-17 10:50 ` [PATCH 4/5] ARM: sti: Always enable CLKSRC_ST_LPC_CLOCK Peter Griffin
2015-04-17 10:50 ` [PATCH 5/5] ARM: DT: STi: STiH407: Add DT node for st-lpc timer Peter Griffin
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