Le 19/09/2022 à 09:02, Johan Hovold a écrit :
On Sun, Sep 18, 2022 at 03:08:17PM +0200, Christophe JAILLET wrote:
When the 'struct applespi_data' structure is allocated at the beginning of
applespi_probe(), 2504 bytes are allocated.
Because of the way memory is allocated, it ends to a 4096 bytes allocation.
So, about 1500 bytes are wasted.
Later in this function, when 'tx_buffer', 'tx_status', 'rx_buffer' and
'msg_buf' are allocated, 256, 4, 256 and 512 bytes are requested (~1 ko).
A devm_ memory allocation has a small overhead of 40 bytes. So, for the
same reason as above, it ends to allocate 512, 64, 512 and 1024 (~2 ko).
All that said, defining these 4 arrays as part of 'struct applespi_data'
saves 2 ko of runtime memory.
3504 bytes are now requested, and 4096 really allocated. All these 4
arrays fit in the 'wasted' memory of the first allocation.
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
---
Compile tested only.
---
drivers/input/keyboard/applespi.c | 23 ++++-------------------
1 file changed, 4 insertions(+), 19 deletions(-)
diff --git a/drivers/input/keyboard/applespi.c b/drivers/input/keyboard/applespi.c
index fab5473ae5da..bee4ccfa2b05 100644
--- a/drivers/input/keyboard/applespi.c
+++ b/drivers/input/keyboard/applespi.c
@@ -373,11 +373,11 @@ struct applespi_data {
struct input_dev *keyboard_input_dev;
struct input_dev *touchpad_input_dev;
- u8 *tx_buffer;
- u8 *tx_status;
- u8 *rx_buffer;
+ u8 tx_buffer[APPLESPI_PACKET_SIZE];
+ u8 tx_status[APPLESPI_STATUS_SIZE];
+ u8 rx_buffer[APPLESPI_PACKET_SIZE];
- u8 *msg_buf;
+ u8 msg_buf[MAX_PKTS_PER_MSG * APPLESPI_PACKET_SIZE];
unsigned int saved_msg_len;
struct applespi_tp_info tp_info;
This kind of change is generally broken in case DMA can be involved.
Allocating the transfer buffers separately makes sure that alignment
requirements are met and avoids hard-to-debug memory corruption issues.
Johan
Got it. I'll keep away from it.
Thanks for the feed-back and explanation.
CJ
