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Date: Mon, 08 Mar 2021 14:46:26 +0000
From: Paul Cercueil <paul@...pouillou.net>
To: Michael Turquette <mturquette@...libre.com>,
Stephen Boyd <sboyd@...nel.org>,
Ulf Hansson <ulf.hansson@...aro.org>,
Russell King <linux@...linux.org.uk>
Cc: od@...c.me, linux-clk@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
linux-mmc@...r.kernel.org
Subject: Re: [PATCH 2/2] mmc: jz4740: Add support for monitoring PLL clock
rate changes
Le dim. 7 mars 2021 à 17:07, Paul Cercueil <paul@...pouillou.net> a
écrit :
> The main PLL can have its rate changed at any moment. To keep the MMC
> clock running at a rate that fits the specifications, we need to
> recompute the MMC clock rate every time the PLL rate changes.
>
> Use a mutex to ensure that the MMC is idle before performing the PLL
> and
> MMC rate changes.
>
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
> drivers/mmc/host/jz4740_mmc.c | 70
> ++++++++++++++++++++++++++++++++++-
> 1 file changed, 69 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/host/jz4740_mmc.c
> b/drivers/mmc/host/jz4740_mmc.c
> index b3c636edbb46..1197b8c6b6ed 100644
> --- a/drivers/mmc/host/jz4740_mmc.c
> +++ b/drivers/mmc/host/jz4740_mmc.c
> @@ -18,6 +18,7 @@
> #include <linux/mmc/host.h>
> #include <linux/mmc/slot-gpio.h>
> #include <linux/module.h>
> +#include <linux/mutex.h>
> #include <linux/of_device.h>
> #include <linux/pinctrl/consumer.h>
> #include <linux/platform_device.h>
> @@ -149,6 +150,10 @@ struct jz4740_mmc_host {
> struct platform_device *pdev;
> struct clk *clk;
>
> + atomic_t clk_mutex_count;
> + struct mutex clk_mutex;
> + struct notifier_block clock_nb;
> +
> enum jz4740_mmc_version version;
>
> int irq;
> @@ -338,6 +343,9 @@ static void jz4740_mmc_pre_request(struct
> mmc_host *mmc,
> struct jz4740_mmc_host *host = mmc_priv(mmc);
> struct mmc_data *data = mrq->data;
>
> + if (atomic_inc_and_test(&host->clk_mutex_count))
> + mutex_lock(&host->clk_mutex);
There's an obvious race here, let me rewrite this using the proper
locking mechanism.
-Paul
> +
> if (!host->use_dma)
> return;
>
> @@ -353,6 +361,9 @@ static void jz4740_mmc_post_request(struct
> mmc_host *mmc,
> struct jz4740_mmc_host *host = mmc_priv(mmc);
> struct mmc_data *data = mrq->data;
>
> + if (atomic_dec_return(&host->clk_mutex_count) == -1)
> + mutex_unlock(&host->clk_mutex);
> +
> if (data && data->host_cookie != COOKIE_UNMAPPED)
> jz4740_mmc_dma_unmap(host, data);
>
> @@ -955,6 +966,48 @@ static const struct mmc_host_ops jz4740_mmc_ops
> = {
> .enable_sdio_irq = jz4740_mmc_enable_sdio_irq,
> };
>
> +static inline struct jz4740_mmc_host *
> +jz4740_mmc_nb_get_priv(struct notifier_block *nb)
> +{
> + return container_of(nb, struct jz4740_mmc_host, clock_nb);
> +}
> +
> +static struct clk *jz4740_mmc_get_parent_clk(struct clk *clk)
> +{
> + /*
> + * Return the first clock above the one that will effectively modify
> + * its rate when clk_set_rate(clk) is called.
> + */
> + clk = clk_get_first_to_set_rate(clk);
> +
> + return clk_get_parent(clk);
> +}
> +
> +static int jz4740_mmc_update_clk(struct notifier_block *nb,
> + unsigned long action,
> + void *data)
> +{
> + struct jz4740_mmc_host *host = jz4740_mmc_nb_get_priv(nb);
> +
> + /*
> + * PLL may have changed its frequency; our clock may be running
> above
> + * spec. Wait until MMC is idle (using host->clk_mutex) before
> changing
> + * the PLL clock, and after it's done, reset our clock rate.
> + */
> +
> + switch (action) {
> + case PRE_RATE_CHANGE:
> + mutex_lock(&host->clk_mutex);
> + break;
> + default:
> + clk_set_rate(host->clk, host->mmc->f_max);
> + mutex_unlock(&host->clk_mutex);
> + break;
> + }
> +
> + return NOTIFY_OK;
> +}
> +
> static const struct of_device_id jz4740_mmc_of_match[] = {
> { .compatible = "ingenic,jz4740-mmc", .data = (void *)
> JZ_MMC_JZ4740 },
> { .compatible = "ingenic,jz4725b-mmc", .data = (void
> *)JZ_MMC_JZ4725B },
> @@ -971,6 +1024,7 @@ static int jz4740_mmc_probe(struct
> platform_device* pdev)
> struct mmc_host *mmc;
> struct jz4740_mmc_host *host;
> const struct of_device_id *match;
> + struct clk *parent_clk;
>
> mmc = mmc_alloc_host(sizeof(struct jz4740_mmc_host), &pdev->dev);
> if (!mmc) {
> @@ -1058,12 +1112,24 @@ static int jz4740_mmc_probe(struct
> platform_device* pdev)
> goto err_free_irq;
> host->use_dma = !ret;
>
> + atomic_set(&host->clk_mutex_count, -1);
> + mutex_init(&host->clk_mutex);
> + host->clock_nb.notifier_call = jz4740_mmc_update_clk;
> +
> + parent_clk = jz4740_mmc_get_parent_clk(host->clk);
> +
> + ret = clk_notifier_register(parent_clk, &host->clock_nb);
> + if (ret) {
> + dev_err(&pdev->dev, "Unable to register clock notifier\n");
> + goto err_release_dma;
> + }
> +
> platform_set_drvdata(pdev, host);
> ret = mmc_add_host(mmc);
>
> if (ret) {
> dev_err(&pdev->dev, "Failed to add mmc host: %d\n", ret);
> - goto err_release_dma;
> + goto err_unregister_clk_notifier;
> }
> dev_info(&pdev->dev, "Ingenic SD/MMC card driver registered\n");
>
> @@ -1074,6 +1140,8 @@ static int jz4740_mmc_probe(struct
> platform_device* pdev)
>
> return 0;
>
> +err_unregister_clk_notifier:
> + clk_notifier_unregister(parent_clk, &host->clock_nb);
> err_release_dma:
> if (host->use_dma)
> jz4740_mmc_release_dma_channels(host);
> --
> 2.30.1
>
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