Re: [PATCH RESEND v4] mmc: core: Remove bounce buffer in mmc_send_cxd_data()

From: kyungsik.lee
Date: Thu Aug 02 2012 - 01:40:32 EST

Hello Chanho Min,


On 2012-08-02 ìì 11:50, Chanho Min wrote:
-----Original Message-----
From: Kyungsik Lee [mailto:kyungsik.lee@xxxxxxx]
Sent: Wednesday, August 01, 2012 10:06 AM
To: Chris Ball
Cc: Venkatraman S; Jaehoon Chung; raphael.andy.lee@xxxxxxxxx; linux-
mmc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Kyungsik Lee
Subject: [PATCH RESEND v4] mmc: core: Remove bounce buffer in
mmc_send_cxd_data()

It is expected that Extended CSD register(the size of this register
is larger than CID/CSD) will be referenced more frequently as more
fields have been added to Extended CSD and it seems that it is not
a good option to double the memory used.

This patch is intended to avoid the use of bounce buffer for reading
Extended CSD register in mmc_send_cxd_data().

Signed-off-by: Kyungsik Lee <kyungsik.lee@xxxxxxx>
Signed-off-by: S, Venkatraman <svenkatr@xxxxxx>
---
Changes in v2:
- Handling on-stack buffer if it's used in caller.

Changes in v3:
- Remove unnecesary code.

Changes in v4:
- Modify codes based-on S, Venkatraman's comments.
---
drivers/mmc/core/mmc_ops.c | 54
+++++++++++++++++++++++++++++++------------
-
1 files changed, 38 insertions(+), 16 deletions(-)

diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
index 0ed2cc5..920a017 100644
--- a/drivers/mmc/core/mmc_ops.c
+++ b/drivers/mmc/core/mmc_ops.c
@@ -239,13 +239,19 @@ mmc_send_cxd_data(struct mmc_card *card, struct
mmc_host
*host,
struct mmc_data data = {0};
struct scatterlist sg;
void *data_buf;
+ int is_on_stack;

- /* dma onto stack is unsafe/nonportable, but callers to this
- * routine normally provide temporary on-stack buffers ...
- */
- data_buf = kmalloc(len, GFP_KERNEL);
- if (data_buf == NULL)
- return -ENOMEM;
+ is_on_stack = object_is_on_stack(buf);
+ if (is_on_stack) {
+
+ /* dma onto stack is unsafe/nonportable, but callers to this
+ * routine normally provide temporary on-stack buffers ...
+ */
+ data_buf = kmalloc(len, GFP_KERNEL);
+ if (data_buf == NULL)
+ return -ENOMEM;
+ } else
+ data_buf = buf;

mrq.cmd = &cmd;
mrq.data = &data;
@@ -280,8 +286,10 @@ mmc_send_cxd_data(struct mmc_card *card, struct
mmc_host
*host,

mmc_wait_for_req(host, &mrq);

- memcpy(buf, data_buf, len);
- kfree(data_buf);
+ if (is_on_stack) {
+ memcpy(buf, data_buf, len);
+ kfree(data_buf);
+ }

if (cmd.error)
return cmd.error;
@@ -294,24 +302,32 @@ mmc_send_cxd_data(struct mmc_card *card, struct
mmc_host
*host,
int mmc_send_csd(struct mmc_card *card, u32 *csd)
{
int ret, i;
+ u32 *csd_tmp;

if (!mmc_host_is_spi(card->host))
return mmc_send_cxd_native(card->host, card->rca << 16,
csd, MMC_SEND_CSD);

- ret = mmc_send_cxd_data(card, card->host, MMC_SEND_CSD, csd, 16);
+ csd_tmp = kmalloc(16, GFP_KERNEL);
+ if (!csd_tmp)
+ return -ENOMEM;
+
+ ret = mmc_send_cxd_data(card, card->host, MMC_SEND_CSD, csd_tmp,
16);
if (ret)
- return ret;
+ goto err;

for (i = 0;i < 4;i++)
- csd[i] = be32_to_cpu(csd[i]);
+ csd[i] = be32_to_cpu(csd_tmp[i]);

- return 0;
+err:
+ kfree(csd_tmp);
+ return ret;
}
If we can handle for the on-stack buffer in mmc_send_cxd_data, why do we
need callers's modification as bellows?
As you comment above, on-stack buffer can be handled with no better performance gain.
In case of both mmc_send_cid() and mmc_send_csd(), on-stack buffers have not been allocated
in the upper callers to the two functions(you may check it in the upper callers).
And you will find out the reason why such a modification below is needed in the mail thread
(Reply to S, Venkatraman's comment).

Thanks
Kyungsik Lee
int mmc_send_cid(struct mmc_host *host, u32 *cid)
{
int ret, i;
+ u32 *cid_tmp;

if (!mmc_host_is_spi(host)) {
if (!host->card)
@@ -320,14 +336,20 @@ int mmc_send_cid(struct mmc_host *host, u32 *cid)
cid, MMC_SEND_CID);
}

- ret = mmc_send_cxd_data(NULL, host, MMC_SEND_CID, cid, 16);
+ cid_tmp = kmalloc(16, GFP_KERNEL);
+ if (!cid_tmp)
+ return -ENOMEM;
+
+ ret = mmc_send_cxd_data(NULL, host, MMC_SEND_CID, cid_tmp, 16);
if (ret)
- return ret;
+ goto err;

for (i = 0;i < 4;i++)
- cid[i] = be32_to_cpu(cid[i]);
+ cid[i] = be32_to_cpu(cid_tmp[i]);

- return 0;
+err:
+ kfree(cid_tmp);
+ return ret;
}

int mmc_send_ext_csd(struct mmc_card *card, u8 *ext_csd)
--
1.7.0.4
Thanks
Chanho Min



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/