linux-kernel - Re: [PATCH 5/7] mmc_spi: allow higher timeouts for SPI mode

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Date:	Wed, 11 Mar 2009 14:02:19 +0000
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Wolfgang Mües <wolfgang.mues@...rswald.de>
Cc:	Pierre Ossman <drzeus@...eus.cx>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Mike Frysinger <vapier.adi@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] mmc_spi: allow higher timeouts for SPI mode

On Wed, Mar 11, 2009 at 02:28:39PM +0100, Wolfgang Mües wrote:
> From: Wolfgang Muees <wolfgang.mues@...rswald.de>
> 
> o Some SD cards have very high timeouts in SPI mode.
>   So adjust the timeouts from theory to practice.
> 

[...]

> +	/*
> +	 * Some cards need very high timeouts if driven in SPI mode.
> +	 * The worst observed timeout was 900ms after writing a
> +	 * continuous stream of data until the internal logic
> +	 * overflowed.
> +	 */
> +	if (mmc_host_is_spi(card->host)) {
> +		if (data->flags & MMC_DATA_WRITE) {
> +			if (data->timeout_ns < 1000000000)
> +				data->timeout_ns = 1000000000;	/* 1s */

I am correct in thinking that this patch, in conjuction with your other
patch, "[PATCH 6/7] mmc_spi: convert timeout handling to jiffies and avoid 
busy waiting", will now penalize my working card and mandate a timeout
of 1 second?

Without your patch 6 at least mmc_spi_skip() would busy-wait for the
response, and if my card completed in less than 1 second then it'd just
return quicker.

It seems you've introduced a performance hit on all MMC over SPI cards.
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