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Message-ID: <5400211D.1060107@topic.nl>
Date: Fri, 29 Aug 2014 08:43:41 +0200
From: Mike Looijmans <mike.looijmans@...ic.nl>
To: linux-mmc@...r.kernel.org
CC: cjb@...top.org, ulf.hansson@...aro.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] davinci-mmc: Use IRQ to detect "card not busy" status
change
Note: I have not been able to test or even compile this on recent
kernels. Can somebody verify that this does not kill the SD driver?
Mike.
On 08/29/2014 08:41 AM, Mike Looijmans wrote:
> The davinci-mmc driver uses a busy wait loop to wait for the card to
> become ready (BUSY signal). The MMC card uses this to signal the
> controller that it's busy writing and cannot handle new requests yet.
> This loop often takes 100k cycles and 10ms to complete.
>
> The controller can raise an interrupt when the BUSY signal is deasserted,
> so the routine has been adapted to trigger an interrupt and wait for it
> using a wait_event_timeout instead of a busy wait loop.
>
> This reduces the CPU usage of the mmcqd process drastically, from 35% to
> 2% when writing to SD. No noticable change in performance or reliability.
>
> Tested on a custom board with an OMAP-L138 CPU. Patch originally applied
> to a 2.6.37 kernel and ported to 3.14.
>
> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
> ---
> drivers/mmc/host/davinci_mmc.c | 52 +++++++++++++++++++++++++---------------
> 1 file changed, 33 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/mmc/host/davinci_mmc.c b/drivers/mmc/host/davinci_mmc.c
> index d615374..50458f4 100644
> --- a/drivers/mmc/host/davinci_mmc.c
> +++ b/drivers/mmc/host/davinci_mmc.c
> @@ -223,6 +223,7 @@ struct mmc_davinci_host {
> #ifdef CONFIG_CPU_FREQ
> struct notifier_block freq_transition;
> #endif
> + wait_queue_head_t wait_while_busy_queue
> };
>
> static irqreturn_t mmc_davinci_irq(int irq, void *dev_id);
> @@ -628,23 +629,28 @@ mmc_davinci_prepare_data(struct mmc_davinci_host *host, struct mmc_request *req)
> static void mmc_davinci_request(struct mmc_host *mmc, struct mmc_request *req)
> {
> struct mmc_davinci_host *host = mmc_priv(mmc);
> - unsigned long timeout = jiffies + msecs_to_jiffies(900);
> - u32 mmcst1 = 0;
> + unsigned int remaining;
>
> /* Card may still be sending BUSY after a previous operation,
> * typically some kind of write. If so, we can't proceed yet.
> */
> - while (time_before(jiffies, timeout)) {
> - mmcst1 = readl(host->base + DAVINCI_MMCST1);
> - if (!(mmcst1 & MMCST1_BUSY))
> - break;
> - cpu_relax();
> - }
> - if (mmcst1 & MMCST1_BUSY) {
> - dev_err(mmc_dev(host->mmc), "still BUSY? bad ... \n");
> - req->cmd->error = -ETIMEDOUT;
> - mmc_request_done(mmc, req);
> - return;
> + if (readl(host->base + DAVINCI_MMCST1) & MMCST1_BUSY) {
> + /* Arm BSYDNE interrupt and wait for it */
> + writel(MMCST0_BSYDNE, host->base + DAVINCI_MMCIM);
> + remaining = wait_event_timeout(
> + host->wait_while_busy_queue,
> + ((readl(host->base + DAVINCI_MMCST1) & MMCST1_BUSY) == 0),
> + msecs_to_jiffies(900));
> + writel(0, host->base + DAVINCI_MMCIM);
> + if (unlikely(remaining == 0))
> + {
> + if (readl(host->base + DAVINCI_MMCST1) & MMCST1_BUSY) {
> + dev_err(mmc_dev(host->mmc), "Timeout waiting for BSYDNE interrupt.\n");
> + req->cmd->error = -ETIMEDOUT;
> + mmc_request_done(mmc, req);
> + return;
> + }
> + }
> }
>
> host->do_dma = 0;
> @@ -914,18 +920,21 @@ static irqreturn_t mmc_davinci_irq(int irq, void *dev_id)
> int end_transfer = 0;
> struct mmc_data *data = host->data;
>
> + status = readl(host->base + DAVINCI_MMCST0);
> + qstatus = status;
> +
> if (host->cmd == NULL && host->data == NULL) {
> - status = readl(host->base + DAVINCI_MMCST0);
> - dev_dbg(mmc_dev(host->mmc),
> - "Spurious interrupt 0x%04x\n", status);
> + /* We may have been waiting for the busy-done signal */
> + if (qstatus & MMCST0_BSYDNE) {
> + wake_up(&host->wait_while_busy_queue);
> + return IRQ_HANDLED;
> + }
> + dev_dbg(mmc_dev(host->mmc), "Spurious interrupt %#x\n", status);
> /* Disable the interrupt from mmcsd */
> writel(0, host->base + DAVINCI_MMCIM);
> return IRQ_NONE;
> }
>
> - status = readl(host->base + DAVINCI_MMCST0);
> - qstatus = status;
> -
> /* handle FIFO first when using PIO for data.
> * bytes_left will decrease to zero as I/O progress and status will
> * read zero over iteration because this controller status
> @@ -1044,6 +1053,10 @@ static irqreturn_t mmc_davinci_irq(int irq, void *dev_id)
> end_command = (int) host->cmd;
> }
>
> + if (qstatus & MMCST0_BSYDNE) {
> + wake_up(&host->wait_while_busy_queue);
> + }
> +
> if (end_command)
> mmc_davinci_cmd_done(host, host->cmd);
> if (end_transfer)
> @@ -1261,6 +1274,7 @@ static int __init davinci_mmcsd_probe(struct platform_device *pdev)
>
> host = mmc_priv(mmc);
> host->mmc = mmc; /* Important */
> + init_waitqueue_head(&host->wait_while_busy_queue);
>
> r = platform_get_resource(pdev, IORESOURCE_DMA, 0);
> if (!r)
>
--
Mike Looijmans
--
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