linux-kernel - Re: [PATCHv2 3/5] mmc: shdci-bcm2835: add efficient back-to-back write workaround

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Message-ID: <5459AE2C.2050401@wwwdotorg.org>
Date:	Tue, 04 Nov 2014 21:57:16 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Scott Branden <sbranden@...adcom.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Peter Griffin <peter.griffin@...aro.org>,
	Chris Ball <chris@...ntf.net>,
	Piotr Krol <pietrushnic@...il.com>
CC:	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Joe Perches <joe@...ches.com>,
	linux-rpi-kernel@...ts.infradead.org, Ray Jui <rjui@...adcom.com>,
	bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCHv2 3/5] mmc: shdci-bcm2835: add efficient back-to-back
 write workaround

On 10/30/2014 12:36 AM, Scott Branden wrote:
> The bcm2835 has clock domain issues when back to back writes to certain
> registers are written.  The existing driver works around this issue with
> udelay.  A more efficient method is to store the 8 and 16 bit writes
> to the registers affected and then write them as 32 bits at the appropriate
> time.

> diff --git a/drivers/mmc/host/sdhci-bcm2835.c b/drivers/mmc/host/sdhci-bcm2835.c

>  static void bcm2835_sdhci_writew(struct sdhci_host *host, u16 val, int reg)
>  {
>  	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> -	struct bcm2835_sdhci *bcm2835_host = pltfm_host->priv;
> -	u32 oldval = (reg == SDHCI_COMMAND) ? bcm2835_host->shadow :
> -		bcm2835_sdhci_readl(host, reg & ~3);
> +	struct bcm2835_sdhci_host *bcm2835_host = pltfm_host->priv;

Is that type change for bcm2835_host really correct?

> +	} else {
> +		/* Read reg, all other registers are not shadowed */
> +		oldval = readl(host->ioaddr + (reg & ~3));

Is there any reason to use readl() directly here rather than calling
bcm2835_readl()? ...

>  static void bcm2835_sdhci_writeb(struct sdhci_host *host, u8 val, int reg)
>  {
> -	u32 oldval = bcm2835_sdhci_readl(host, reg & ~3);
> +	u32 oldval = readl(host->ioaddr + (reg & ~3));

... and here in particular, since this seems like an unrelated change?

>  static int bcm2835_sdhci_probe(struct platform_device *pdev)
>  {
>  	struct sdhci_host *host;
> -	struct bcm2835_sdhci *bcm2835_host;
> +	struct bcm2835_sdhci_host *bcm2835_host;

Is that type change for bcm2835_host really correct?
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