[PATCH] Remove large struct from stack in DVB dib3000mc and dib7000p drivers

[imunsie@au1.ibm.com]

From: Ian Munsie <imunsie@au.ibm.com>

Compiling these drivers results in the following compiler warnings on
PowerPC 64 bit:

drivers/media/dvb/frontends/dib3000mc.c:853: warning: the frame size of 2208 bytes is larger than 2048 bytes
drivers/media/dvb/frontends/dib7000p.c:1367: warning: the frame size of 2288 bytes is larger than 2048 bytes

The <driver>_i2c_enumeration functions use a large struct to hold the
state, which is stored on the stack.

This patch allocates that structure dynamically instead, thereby
conserving the driver's use of the stack.

There is now the possibility that these functions will return -ENOMEM in
case the dynamic memory allocation fails and while a useful message will
show up in dmesg, at the moment the -ENOMEM condition is not relayed
all the way back to userspace and it will receive an -ENODEV instead.
Is it worth pursuing returning the correct error all the way up to
userspace?

Signed-off-by: Ian Munsie <imunsie@au.ibm.com>
---
 drivers/media/dvb/frontends/dib3000mc.c |   43 +++++++++++++++++++-----------
 drivers/media/dvb/frontends/dib7000p.c  |   44 +++++++++++++++++++-----------
 2 files changed, 55 insertions(+), 32 deletions(-)

diff --git a/drivers/media/dvb/frontends/dib3000mc.c b/drivers/media/dvb/frontends/dib3000mc.c
index fa85160..78c2813 100644
--- a/drivers/media/dvb/frontends/dib3000mc.c
+++ b/drivers/media/dvb/frontends/dib3000mc.c
@@ -13,6 +13,7 @@
 
 #include <linux/kernel.h>
 #include <linux/i2c.h>
+#include <linux/slab.h>
 
 #include "dvb_frontend.h"
 
@@ -813,43 +814,53 @@ EXPORT_SYMBOL(dib3000mc_set_config);
 
 int dib3000mc_i2c_enumeration(struct i2c_adapter *i2c, int no_of_demods, u8 default_addr, struct dib3000mc_config cfg[])
 {
-	struct dib3000mc_state st = { .i2c_adap = i2c };
+	struct dib3000mc_state *st;
 	int k;
 	u8 new_addr;
-
 	static u8 DIB3000MC_I2C_ADDRESS[] = {20,22,24,26};
+	int ret = 0;
+
+	st = kzalloc(sizeof(struct dib3000mc_state), GFP_KERNEL);
+	if (!st) {
+		dprintk(KERN_ERR "Out of memory allocating dib3000mc_state in %s", __func__);
+		return -ENOMEM;
+	}
+	st->i2c_adap = i2c;
 
 	for (k = no_of_demods-1; k >= 0; k--) {
-		st.cfg = &cfg[k];
+		st->cfg = &cfg[k];
 
 		/* designated i2c address */
 		new_addr          = DIB3000MC_I2C_ADDRESS[k];
-		st.i2c_addr = new_addr;
-		if (dib3000mc_identify(&st) != 0) {
-			st.i2c_addr = default_addr;
-			if (dib3000mc_identify(&st) != 0) {
+		st->i2c_addr = new_addr;
+		if (dib3000mc_identify(st) != 0) {
+			st->i2c_addr = default_addr;
+			if (dib3000mc_identify(st) != 0) {
 				dprintk("-E-  DiB3000P/MC #%d: not identified\n", k);
-				return -ENODEV;
+				ret = -ENODEV;
+				goto out;
 			}
 		}
 
-		dib3000mc_set_output_mode(&st, OUTMODE_MPEG2_PAR_CONT_CLK);
+		dib3000mc_set_output_mode(st, OUTMODE_MPEG2_PAR_CONT_CLK);
 
 		// set new i2c address and force divstr (Bit 1) to value 0 (Bit 0)
-		dib3000mc_write_word(&st, 1024, (new_addr << 3) | 0x1);
-		st.i2c_addr = new_addr;
+		dib3000mc_write_word(st, 1024, (new_addr << 3) | 0x1);
+		st->i2c_addr = new_addr;
 	}
 
 	for (k = 0; k < no_of_demods; k++) {
-		st.cfg = &cfg[k];
-		st.i2c_addr = DIB3000MC_I2C_ADDRESS[k];
+		st->cfg = &cfg[k];
+		st->i2c_addr = DIB3000MC_I2C_ADDRESS[k];
 
-		dib3000mc_write_word(&st, 1024, st.i2c_addr << 3);
+		dib3000mc_write_word(st, 1024, st->i2c_addr << 3);
 
 		/* turn off data output */
-		dib3000mc_set_output_mode(&st, OUTMODE_HIGH_Z);
+		dib3000mc_set_output_mode(st, OUTMODE_HIGH_Z);
 	}
-	return 0;
+out:
+	kfree(st);
+	return ret;
 }
 EXPORT_SYMBOL(dib3000mc_i2c_enumeration);
 
diff --git a/drivers/media/dvb/frontends/dib7000p.c b/drivers/media/dvb/frontends/dib7000p.c
index 750ae61..08d47f2 100644
--- a/drivers/media/dvb/frontends/dib7000p.c
+++ b/drivers/media/dvb/frontends/dib7000p.c
@@ -9,6 +9,7 @@
  */
 #include <linux/kernel.h>
 #include <linux/i2c.h>
+#include <linux/slab.h>
 
 #include "dvb_math.h"
 #include "dvb_frontend.h"
@@ -1323,47 +1324,58 @@ EXPORT_SYMBOL(dib7000p_pid_filter);
 
 int dib7000p_i2c_enumeration(struct i2c_adapter *i2c, int no_of_demods, u8 default_addr, struct dib7000p_config cfg[])
 {
-	struct dib7000p_state st = { .i2c_adap = i2c };
+	struct dib7000p_state *st;
 	int k = 0;
 	u8 new_addr = 0;
+	int ret = 0;
+
+	st = kzalloc(sizeof(struct dib7000p_state), GFP_KERNEL);
+	if (!st) {
+		dprintk(KERN_ERR "Out of memory allocating dib7000p_state in %s", __func__);
+		return -ENOMEM;
+	}
+	st->i2c_adap = i2c;
 
 	for (k = no_of_demods-1; k >= 0; k--) {
-		st.cfg = cfg[k];
+		st->cfg = cfg[k];
 
 		/* designated i2c address */
 		new_addr          = (0x40 + k) << 1;
-		st.i2c_addr = new_addr;
-		dib7000p_write_word(&st, 1287, 0x0003); /* sram lead in, rdy */
-		if (dib7000p_identify(&st) != 0) {
-			st.i2c_addr = default_addr;
-			dib7000p_write_word(&st, 1287, 0x0003); /* sram lead in, rdy */
-			if (dib7000p_identify(&st) != 0) {
+		st->i2c_addr = new_addr;
+		dib7000p_write_word(st, 1287, 0x0003); /* sram lead in, rdy */
+		if (dib7000p_identify(st) != 0) {
+			st->i2c_addr = default_addr;
+			dib7000p_write_word(st, 1287, 0x0003); /* sram lead in, rdy */
+			if (dib7000p_identify(st) != 0) {
 				dprintk("DiB7000P #%d: not identified\n", k);
-				return -EIO;
+				ret = -EIO;
+				goto out;
 			}
 		}
 
 		/* start diversity to pull_down div_str - just for i2c-enumeration */
-		dib7000p_set_output_mode(&st, OUTMODE_DIVERSITY);
+		dib7000p_set_output_mode(st, OUTMODE_DIVERSITY);
 
 		/* set new i2c address and force divstart */
-		dib7000p_write_word(&st, 1285, (new_addr << 2) | 0x2);
+		dib7000p_write_word(st, 1285, (new_addr << 2) | 0x2);
 
 		dprintk("IC %d initialized (to i2c_address 0x%x)", k, new_addr);
 	}
 
 	for (k = 0; k < no_of_demods; k++) {
-		st.cfg = cfg[k];
-		st.i2c_addr = (0x40 + k) << 1;
+		st->cfg = cfg[k];
+		st->i2c_addr = (0x40 + k) << 1;
 
 		// unforce divstr
-		dib7000p_write_word(&st, 1285, st.i2c_addr << 2);
+		dib7000p_write_word(st, 1285, st->i2c_addr << 2);
 
 		/* deactivate div - it was just for i2c-enumeration */
-		dib7000p_set_output_mode(&st, OUTMODE_HIGH_Z);
+		dib7000p_set_output_mode(st, OUTMODE_HIGH_Z);
 	}
 
-	return 0;
+out:
+	kfree(st);
+	return ret;
 }
 EXPORT_SYMBOL(dib7000p_i2c_enumeration);
 
-- 
1.6.6.1