linux-kernel - Re: [PATCH v2 2/2] memory: samsung: exynos5422-dmc: Add module param to control IRQ mode

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Date:   Tue, 14 Jul 2020 09:42:05 +0200
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, willy.mh.wolff.ml@...il.com,
        k.konieczny@...sung.com, cw00.choi@...sung.com, krzk@...nel.org,
        chanwoo@...nel.org, myungjoo.ham@...sung.com,
        kyungmin.park@...sung.com, s.nawrocki@...sung.com, kgene@...nel.org
Subject: Re: [PATCH v2 2/2] memory: samsung: exynos5422-dmc: Add module
 param to control IRQ mode


Hi,

On 7/10/20 9:11 PM, Lukasz Luba wrote:
> The driver can operate in two modes relaying on devfreq monitoring
> mechanism which periodically checks the device status or it can use
> interrupts when they are provided by loaded Device Tree. The newly
> introduced module parameter can be used to choose between devfreq
> monitoring and internal interrupts without modifying the Device Tree.
> It also sets devfreq monitoring as default when the parameter is not set
> (also the case for default when the driver is not built as a module).

Could you please explain why should we leave the IRQ mode
support in the dmc driver?

What are the advantages over the polling mode?

In what scenarios it should be used?

[ If this is only for documentation purposes then it should be
  removed as it would stay in (easily accessible) git history
  anyway.. ]

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

> Reported-by: Willy Wolff <willy.mh.wolff.ml@...il.com>
> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> ---
>  drivers/memory/samsung/exynos5422-dmc.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/memory/samsung/exynos5422-dmc.c b/drivers/memory/samsung/exynos5422-dmc.c
> index e03ee35f0ab5..53bfe6b7b703 100644
> --- a/drivers/memory/samsung/exynos5422-dmc.c
> +++ b/drivers/memory/samsung/exynos5422-dmc.c
> @@ -12,6 +12,7 @@
>  #include <linux/io.h>
>  #include <linux/mfd/syscon.h>
>  #include <linux/module.h>
> +#include <linux/moduleparam.h>
>  #include <linux/of_device.h>
>  #include <linux/pm_opp.h>
>  #include <linux/platform_device.h>
> @@ -21,6 +22,10 @@
>  #include "../jedec_ddr.h"
>  #include "../of_memory.h"
>  
> +static int irqmode;
> +module_param(irqmode, int, 0644);
> +MODULE_PARM_DESC(irqmode, "Enable IRQ mode (0=off [default], 1=on)");
> +
>  #define EXYNOS5_DREXI_TIMINGAREF		(0x0030)
>  #define EXYNOS5_DREXI_TIMINGROW0		(0x0034)
>  #define EXYNOS5_DREXI_TIMINGDATA0		(0x0038)
> @@ -1428,7 +1433,7 @@ static int exynos5_dmc_probe(struct platform_device *pdev)
>  	/* There is two modes in which the driver works: polling or IRQ */
>  	irq[0] = platform_get_irq_byname(pdev, "drex_0");
>  	irq[1] = platform_get_irq_byname(pdev, "drex_1");
> -	if (irq[0] > 0 && irq[1] > 0) {
> +	if (irq[0] > 0 && irq[1] > 0 && irqmode) {
>  		ret = devm_request_threaded_irq(dev, irq[0], NULL,
>  						dmc_irq_thread, IRQF_ONESHOT,
>  						dev_name(dev), dmc);
> @@ -1485,7 +1490,7 @@ static int exynos5_dmc_probe(struct platform_device *pdev)
>  	if (dmc->in_irq_mode)
>  		exynos5_dmc_start_perf_events(dmc, PERF_COUNTER_START_VALUE);
>  
> -	dev_info(dev, "DMC initialized\n");
> +	dev_info(dev, "DMC initialized, in irq mode: %d\n", dmc->in_irq_mode);
>  
>  	return 0;
>  
>