linux-kernel - Re: [PATCH] mmc: Test bus-width for old MMC devices (v2)

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Date:	Thu, 16 Dec 2010 18:33:49 -0800
From:	Philip Rakity <prakity@...vell.com>
To:	Chris Ball <cjb@...top.org>
CC:	Takashi Iwai <tiwai@...e.de>, Aries Lee <arieslee@...cron.com>,
	zhangfei gao <zhangfei.gao@...il.com>,
	Qiming Wu <wuqm@...vell.com>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: Test bus-width for old MMC devices (v2)


Chris,

It is not possible for bus_width to be not initialized.  This would imply ARRAY_SIZE(bus_widths) is 1.  Certainly not true.
We could just initialize by changing
+		unsigned idx, bus_width;
to
+		unsigned idx, bus_width = 0;

I wonder what compiler are you using so we can avoid this issue in future.

Philip


+		static unsigned ext_csd_bits[][2] = {
+			{ EXT_CSD_BUS_WIDTH_8, EXT_CSD_DDR_BUS_WIDTH_8 },
+			{ EXT_CSD_BUS_WIDTH_4, EXT_CSD_DDR_BUS_WIDTH_4 },
+			{ EXT_CSD_BUS_WIDTH_1, EXT_CSD_BUS_WIDTH_1 },
+		};
+		static unsigned bus_widths[] = {
+			MMC_BUS_WIDTH_8,
+			MMC_BUS_WIDTH_4,
+			MMC_BUS_WIDTH_1
+		};
+		unsigned idx, bus_width;
+
+		if (host->caps & MMC_CAP_8_BIT_DATA)
+			idx = 0;
+		else
+			idx = 1;
+		for (; idx < ARRAY_SIZE(bus_widths); idx++) {
+			bus_width = bus_widths[idx];
+			if (bus_width == MMC_BUS_WIDTH_1)
+				ddr = 0; /* no DDR for 1-bit width */


On Dec 16, 2010, at 3:40 PM, Chris Ball wrote:

> Hi Takashi,
> 
> On Wed, Dec 15, 2010 at 08:14:24AM +0100, Takashi Iwai wrote:
>> From: Aries Lee <arieslee@...cron.com>
>> 
>> Some old MMC devices fail with the 4/8 bits the driver tries to use
>> exclusively.  This patch adds a test for the given bus setup and falls
>> back to the lower bit mode (until 1-bit mode) when the test fails.
>> 
>> [Major rework and refactoring by tiwai]
>> [Quirk addition and many fixes by prakity]
>> 
>> v1->v2:
>> - Rebased to the code with DDR support, set DDR bit properly
>> - Return always error when bus-switching fallback failed
>> - Define MMC_BUS_TEST_{R|W} in linux/mmc/mmc.h
>> - Add quirk MMC_CAP_BUS_WIDTH_TEST -- default not used for compatibility
>> - Ignore errors on BUS_TEST_W -- improves chances test will work
>> 
>> Signed-off-by: Aries Lee <arieslee@...cron.com>
>> Signed-off-by: Takashi Iwai <tiwai@...e.de>
>> Signed-off-by: Philip Rakity <prakity@...vell.com>
>> Tested-by: Philip Rakity <prakity@...vell.com>
> 
> This looks good, but adds a warning:
> 
> drivers/mmc/core/mmc.c: In function ‘mmc_init_card’:
> drivers/mmc/core/mmc.c:547: warning: ‘bus_width’ may be used uninitialized in this function
> 
> Thanks,
> 
> -- 
> Chris Ball   <cjb@...top.org>   <http://printf.net/>
> One Laptop Per Child

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