Re: [PATCH] dw_mmc: Add Synopsys DesignWare mmc host driver.

[Chris Ball <cjb@laptop.org>]

Hi Will,

On Sun, Dec 12, 2010 at 10:57:44AM +0000, Will Newton wrote:
> > drivers/mmc/host/dw_mmc.c: In function ‘dw_mci_pull_data64’:
> > drivers/mmc/host/dw_mmc.c:998: error: implicit declaration of function ‘__raw_readq’
> >
> > because arch/arm doesn't implement raw versions of these 64-bit accesses.
> > I'm surprised that this driver hasn't been compiled on ARM before!  What
> 
> That particular bit of code has been added since it was last built for
> arm. Our architecture can do 64bit accesses so we implement readq.
> Unfortunately there doesn't seem to be a sane way to conditionalize
> code for architectures that have or don't have readq, so I suspect
> I'll have to just remove that branch of the if statement for now.

(Russell, thanks for the excellent explanation.)

Other drivers (MTD, gpio/basic_mmio_gpio.c, fs/fuse, pcm_oss.c)
conditionalize uses of {read,write}q on BITS_PER_LONG >= 64, so
something like this:

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index 7de6b42..526b5cb 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -988,10 +988,11 @@ static void dw_mci_pull_data32(struct dw_mci *host, void *buf, int cnt)
 		*pData++ = mci_readl(host, DATA);
 		cnt--;
 	}
 }
 
+#if BITS_PER_LONG >= 64
 static void dw_mci_push_data64(struct dw_mci *host, void *buf, int cnt)
 {
 	u64 *pData = (u64 *)buf;
 
 	WARN_ON(cnt % 8 != 0);
@@ -1013,10 +1014,11 @@ static void dw_mci_pull_data64(struct dw_mci *host, void *buf, int cnt)
 	while (cnt > 0) {
 		*pData++ = mci_readq(host, DATA);
 		cnt--;
 	}
 }
+#endif
 
 static void dw_mci_read_data_pio(struct dw_mci *host)
 {
 	struct scatterlist *sg = host->sg;
 	void *buf = sg_virt(sg);
@@ -1591,15 +1593,17 @@ static int dw_mci_probe(struct platform_device *pdev)
 	if (!i) {
 		host->push_data = dw_mci_push_data16;
 		host->pull_data = dw_mci_pull_data16;
 		width = 16;
 		host->data_shift = 1;
+#if BITS_PER_LONG >= 64
 	} else if (i == 2) {
 		host->push_data = dw_mci_push_data64;
 		host->pull_data = dw_mci_pull_data64;
 		width = 64;
 		host->data_shift = 3;
+#endif
 	} else {
 		/* Check for a reserved value, and warn if it is */
 		WARN((i != 1),
 			"HCON reports a reserved host data width!\n"
 			"Defaulting to 32-bit access.\n");


This is only useful if you just want the driver to compile (it compiles
on ARM after the above) and don't expect a working device if you find
the HCON programmed with 64-bit width on an ARM board, though.

Thanks,

-- 
Chris Ball   <cjb@laptop.org>   <http://printf.net/>
One Laptop Per Child