Re: [PATCH 3/3] mtd/nand : workaround for Freescale FCM to support large-page Nand chip

On 12/05/2011 12:47 AM, Artem Bityutskiy wrote:

On Sun, 2011-12-04 at 12:31 +0800, shuo.liu@freescale.com wrote:

quoted

+		/*
+		 * Freescale FCM controller has a 2K size limitation of buffer
+		 * RAM, so elbc_fcm_ctrl->buffer have to be used if writesize
+		 * of chip is greater than 2048.
+		 * We malloc a large enough buffer (maximum page size is 16K).
+		 */
+		elbc_fcm_ctrl->buffer = kmalloc(1024 * 16 + 1024, GFP_KERNEL);
+		if (!elbc_fcm_ctrl->buffer) {
+			dev_err(dev, "failed to allocate memory\n");
+			mutex_unlock(&fsl_elbc_nand_mutex);
+			ret = -ENOMEM;
+			goto err;
+		}

Sorry for returning to this again and agian - I do not have time to dig
suggest you the right solutions on the one hand, you do not provide me a
good answer on the other hand (or I forgot?).

16KiB pages do not even exist I believe.

Googling turns up some hints of it, but nothing concrete such as a
datasheet.  We can assume 8K max for now and adjust it later, as the
need becomes clear.

And you kmalloc 33KiB or RAM

17KiB, or 9KiB if we forget about 16K-page NAND.

although in most cases you need only 5KiB. I think this is wrong -
what is the very strong reason of wasting RAM you have?

Why you cannot allocate exactly the required amount of RAM after
'nand_scan_ident()' finishes and you know the page size?

Because this is a controller resource, shared by multiple NAND chips
that may be different page sizes (even if not, it's adding another point
of synchronization required between initialization of different chips).
 I don't think it's worth the gymnastics to save a few KiB.

-Scott