Re: [PATCH RESEND v2] mmc: core: Remove bounce buffer in mmc_send_cxd_data()

["kyungsik.lee" <kyungsik.lee@xxxxxxx>]

On 2012-07-30 오후 10:16, S, Venkatraman wrote:
> On Mon, Jul 30, 2012 at 7:34 AM, Kyungsik Lee <kyungsik.lee@xxxxxxx> 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@xxxxxxx>
> > ---
> > 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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