linux-kernel - Re: [PATCH RESEND v2] mmc: core: Remove bounce buffer in mmc_send_cxd

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Message-ID: <50172E12.5010002@lge.com>
Date:	Tue, 31 Jul 2012 10:00:02 +0900
From:	"kyungsik.lee" <kyungsik.lee@....com>
To:	"S, Venkatraman" <svenkatr@...com>
CC:	Chris Ball <cjb@...top.org>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	raphael.andy.lee@...il.com, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND v2] mmc: core: Remove bounce buffer in mmc_send_cxd_data()

On 2012-07-30 오후 10:16, S, Venkatraman wrote:
> On Mon, Jul 30, 2012 at 7:34 AM, Kyungsik Lee <kyungsik.lee@....com> wrote:
>> 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().
> Maybe I am reading this wrong, but mmc_send_cid and mmc_send_csd are always
> called with card->raw_cid and card->raw_csd, which are allocated from the heap,
> (from mmc_alloc_card).
> So the second half of your changes are not required, or a WARN_ON
> might suffice ?
In case of non cache-coherent architecture, the address of raw_cid and 
raw_csd should
be aligned on a cache line boundary for DMA. It's not guaranteed all the 
time.
So using kmalloc() is a way to make it work.
>
>> Signed-off-by: Kyungsik Lee <kyungsik.lee@....com>
>> ---
>> Changes in v2:
>> - Handling on-stack buffer if it's used in caller.
>> ---
>>   drivers/mmc/core/mmc_ops.c |   56 ++++++++++++++++++++++++++++++++++---------
>>   1 files changed, 44 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
>> index 0ed2cc5..dae5492 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 +302,37 @@ 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;
>> +
>> +       memcpy(csd, csd_tmp, 16);
>>
>>          for (i = 0;i < 4;i++)
>>                  csd[i] = be32_to_cpu(csd[i]);
>>
>> +       kfree(csd_tmp);
>>          return 0;
>> +
>> +err:
>> +       kfree(csd_tmp);
>> +       return ret;
>>   }
>>
>>   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 +341,25 @@ 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;
>> +
>> +       memcpy(cid, cid_tmp, 16);
>>
>>          for (i = 0;i < 4;i++)
>>                  cid[i] = be32_to_cpu(cid[i]);
>>
>> +       kfree(cid_tmp);
>>          return 0;
>> +
>> +err:
>> +       kfree(cid_tmp);
>> +       return ret;
>>   }
>>
>>   int mmc_send_ext_csd(struct mmc_card *card, u8 *ext_csd)
>> --
>> 1.7.0.4
>>

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