mtd: lpddr: fix excessive stack usage with clang

Building lpddr2_nvm with clang can result in a giant stack usage
in one function:

drivers/mtd/lpddr/lpddr2_nvm.c:399:12: error: stack frame size of 1144 bytes in function 'lpddr2_nvm_probe' [-Werror,-Wframe-larger-than=]

The problem is that clang decides to build a copy of the mtd_info
structure on the stack and then do a memcpy() into the actual version. It
shouldn't really do it that way, but it's not strictly a bug either.

As a workaround, use a static const version of the structure to assign
most of the members upfront and then only set the few members that
require runtime knowledge at probe time.

Fixes: 96ba9dd65788 ("mtd: lpddr: add driver for LPDDR2-NVM PCM memories")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200505140136.263461-1-arnd@arndb.de

diff --git a/drivers/mtd/lpddr/lpddr2_nvm.c b/drivers/mtd/lpddr/lpddr2_nvm.c
index 0f1547f..72f5c7b 100644 (file)
--- a/drivers/mtd/lpddr/lpddr2_nvm.c
+++ b/drivers/mtd/lpddr/lpddr2_nvm.c
@@ -393,6 +393,17 @@ static int lpddr2_nvm_lock(struct mtd_info *mtd, loff_t start_add,
        return lpddr2_nvm_do_block_op(mtd, start_add, len, LPDDR2_NVM_LOCK);
 }
 
+static const struct mtd_info lpddr2_nvm_mtd_info = {
+       .type           = MTD_RAM,
+       .writesize      = 1,
+       .flags          = (MTD_CAP_NVRAM | MTD_POWERUP_LOCK),
+       ._read          = lpddr2_nvm_read,
+       ._write         = lpddr2_nvm_write,
+       ._erase         = lpddr2_nvm_erase,
+       ._unlock        = lpddr2_nvm_unlock,
+       ._lock          = lpddr2_nvm_lock,
+};
+
 /*
  * lpddr2_nvm driver probe method
  */
@@ -433,6 +444,7 @@ static int lpddr2_nvm_probe(struct platform_device *pdev)
                .pfow_base      = OW_BASE_ADDRESS,
                .fldrv_priv     = pcm_data,
        };
+
        if (IS_ERR(map->virt))
                return PTR_ERR(map->virt);
 
@@ -444,22 +456,13 @@ static int lpddr2_nvm_probe(struct platform_device *pdev)
                return PTR_ERR(pcm_data->ctl_regs);
 
        /* Populate mtd_info data structure */
-       *mtd = (struct mtd_info) {
-               .dev            = { .parent = &pdev->dev },
-               .name           = pdev->dev.init_name,
-               .type           = MTD_RAM,
-               .priv           = map,
-               .size           = resource_size(add_range),
-               .erasesize      = ERASE_BLOCKSIZE * pcm_data->bus_width,
-               .writesize      = 1,
-               .writebufsize   = WRITE_BUFFSIZE * pcm_data->bus_width,
-               .flags          = (MTD_CAP_NVRAM | MTD_POWERUP_LOCK),
-               ._read          = lpddr2_nvm_read,
-               ._write         = lpddr2_nvm_write,
-               ._erase         = lpddr2_nvm_erase,
-               ._unlock        = lpddr2_nvm_unlock,
-               ._lock          = lpddr2_nvm_lock,
-       };
+       *mtd = lpddr2_nvm_mtd_info;
+       mtd->dev.parent         = &pdev->dev;
+       mtd->name               = pdev->dev.init_name;
+       mtd->priv               = map;
+       mtd->size               = resource_size(add_range);
+       mtd->erasesize          = ERASE_BLOCKSIZE * pcm_data->bus_width;
+       mtd->writebufsize       = WRITE_BUFFSIZE * pcm_data->bus_width;
 
        /* Verify the presence of the device looking for PFOW string */
        if (!lpddr2_nvm_pfow_present(map)) {