linux-kernel - Re: [PATCH 21/32] mmc: bcm2835-sdhost: Add new driver for the internal SD controller.

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Date:	Thu, 02 Jun 2016 00:18:52 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Gerd Hoffmann <kraxel@...hat.com>
Cc:	linux-rpi-kernel@...ts.infradead.org,
	Eric Anholt <eric@...olt.net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Lee Jones <lee@...nel.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:MULTIMEDIA CARD (MMC), SECURE DIGITAL (SD) AND..." 
	<linux-mmc@...r.kernel.org>,
	"moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 21/32] mmc: bcm2835-sdhost: Add new driver for the internal SD controller.

On Wednesday, June 1, 2016 11:43:30 PM CEST Gerd Hoffmann wrote:

> +static void bcm2835_sdhost_reset_internal(struct bcm2835_host *host)
> +{
> +	u32 temp;
> +
> +	bcm2835_sdhost_set_power(host, false);
> +
> +	bcm2835_sdhost_write(host, 0, SDCMD);
> +	bcm2835_sdhost_write(host, 0, SDARG);
> +	bcm2835_sdhost_write(host, 0xf00000, SDTOUT);
> +	bcm2835_sdhost_write(host, 0, SDCDIV);
> +	bcm2835_sdhost_write(host, 0x7f8, SDHSTS); /* Write 1s to clear */
> +	bcm2835_sdhost_write(host, 0, SDHCFG);
> +	bcm2835_sdhost_write(host, 0, SDHBCT);
> +	bcm2835_sdhost_write(host, 0, SDHBLC);
> +
> +	/* Limit fifo usage due to silicon bug */
> +	temp = bcm2835_sdhost_read(host, SDEDM);
> +	temp &= ~((SDEDM_THRESHOLD_MASK << SDEDM_READ_THRESHOLD_SHIFT) |
> +		  (SDEDM_THRESHOLD_MASK << SDEDM_WRITE_THRESHOLD_SHIFT));
> +	temp |= (FIFO_READ_THRESHOLD << SDEDM_READ_THRESHOLD_SHIFT) |
> +		(FIFO_WRITE_THRESHOLD << SDEDM_WRITE_THRESHOLD_SHIFT);
> +	bcm2835_sdhost_write(host, temp, SDEDM);
> +	mdelay(10);
> +	bcm2835_sdhost_set_power(host, true);
> +	mdelay(10);

Are you sure you cannot use msleep() here?

> +	host->clock = 0;
> +	bcm2835_sdhost_write(host, host->hcfg, SDHCFG);
> +	bcm2835_sdhost_write(host, host->cdiv, SDCDIV);
> +	mmiowb();
> +}

What is the barrier for? Same question for all the other instances

> +
> +static void bcm2835_sdhost_reset(struct mmc_host *mmc)
> +{
> +	struct bcm2835_host *host = mmc_priv(mmc);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&host->lock, flags);
> +	bcm2835_sdhost_reset_internal(host);
> +	spin_unlock_irqrestore(&host->lock, flags);
> +}

The spinlock seems to only protect the reset from happening concurrently
with bcm2835_sdhost_dma_complete() here. So if you ensure that this
function is no longer pending, you can probably use msleep() above.

> +static void bcm2835_sdhost_set_ios(struct mmc_host *mmc, struct mmc_ios *ios);

Maybe rearrange the order of the functions to avoid forward declarations?

> +	spin_lock_init(&host->lock);
> +
> +	if (IS_ERR_OR_NULL(host->dma_chan_tx) ||
> +	    IS_ERR_OR_NULL(host->dma_chan_rx)) {
> +		pr_err("%s: unable to initialise DMA channels. Falling back to PIO\n",
> +		       mmc_hostname(mmc));

When are these ever NULL?

> +	/* Parse OF address directly to get the physical address for
> +	 * DMA to our registers.
> +	 */
> +	host->phys_addr = be32_to_cpup(of_get_address(pdev->dev.of_node, 0,
> +						      NULL, NULL));

This looks broken on 64-bit systems when #address-cells=<2>, or if there
is an intermediate bus with a non-empty ranges property.

What's wrong with platform_get_resource(pdev, IORESOURCE_MEM, 0)?

	Arnd