linux-kernel - Re: [PATCH v3 5/5] mtd: spi-nor: cadence-quadspi: Add runtime PM support

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Date:   Wed, 27 Sep 2017 16:18:49 +0530
From:   Vignesh R <vigneshr@...com>
To:     <matthew.gerlach@...ux.intel.com>
CC:     Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Rob Herring <robh+dt@...nel.org>,
        <linux-mtd@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 5/5] mtd: spi-nor: cadence-quadspi: Add runtime PM
 support

Hi Matthew,

On Tuesday 26 September 2017 05:19 AM, Marek Vasut wrote:
[...]
>>>> Ok thanks! Do you know if pm_runtime_get_sync() can enable clocks for
>>>> QSPI on SoCFPGA or if clk_prepare_enable() is needed? Just trying to see
>>>> if its possible to get rid of clk_*() calls in favor of pm_*() calls.
>>>
>>> Not of the top of my head, sorry. +CC Matthew, he should know.
>>
>> I am not an expert at the clock framework nor the power management, but I
>> did ask around a bit.  No one I asked was planning to change the clk_*()
>> calls to pm_*() call, but the feedback was that it would be a good idea.
> 
> The question is, if we do the replacement, will it break on socfpga ?
> A quick test might be useful.
> 

yes, a quick qspi test with clk_prepare_enable() replaced by pm_*() calls
like below patch would be helpful:


diff --git a/drivers/mtd/spi-nor/cadence-quadspi.c b/drivers/mtd/spi-nor/cadence-quadspi.c
index 53c7d8e0327a..7ad3e176cc88 100644
--- a/drivers/mtd/spi-nor/cadence-quadspi.c
+++ b/drivers/mtd/spi-nor/cadence-quadspi.c
@@ -34,6 +34,7 @@
 #include <linux/sched.h>
 #include <linux/spi/spi.h>
 #include <linux/timer.h>
+#include <linux/pm_runtime.h>
 
 #define CQSPI_NAME                     "cadence-qspi"
 #define CQSPI_MAX_CHIPSELECT           16
@@ -1206,11 +1207,8 @@ static int cqspi_probe(struct platform_device *pdev)
                return -ENXIO;
        }
 
-       ret = clk_prepare_enable(cqspi->clk);
-       if (ret) {
-               dev_err(dev, "Cannot enable QSPI clock.\n");
-               return ret;
-       }
+       pm_runtime_enable(dev);
+       pm_runtime_get_sync(dev);
 
        cqspi->master_ref_clk_hz = clk_get_rate(cqspi->clk);
 
 



-- 
Regards
Vignesh