[PATCH v9 00/12] use nonblock mmc requests to minimize latency

[Per Forlin]

On 26 August 2011 18:28, Santosh <santosh.shilimkar at ti.com> wrote:
> + Balaji,
>
> On Friday 26 August 2011 09:49 PM, Russell King - ARM Linux wrote:
>>
>> I'm not sure who's responsible for this, but the nonblocking MMC stuff is
>> broken on OMAPs HSMMC:
>>
>> mmcblk0: error -84 transferring data, sector 149201, nr 64, cmd response
>> 0x900, card status 0xb00
>> mmcblk0: retrying using single block read
>> ------------[ cut here ]------------
>> WARNING: at /home/rmk/git/linux-2.6-rmk/lib/dma-debug.c:811
>> check_unmap+0x1ac/0x764()
>> omap_hsmmc omap_hsmmc.0: DMA-API: device driver tries to free DMA memory
>> it has not allocated [device address=0x0000000080933000] [size=20480 bytes]
>> Modules linked in:
>> Backtrace:
>> [<c0017874>] (dump_backtrace+0x0/0x10c) from [<c02ce8ac>]
>> (dump_stack+0x18/0x1c)
>>  r7:c1abfcb8 r6:c0186248 r5:c037de51 r4:0000032b
>> [<c02ce894>] (dump_stack+0x0/0x1c) from [<c0039ed4>]
>> (warn_slowpath_common+0x58/0x70)
>> [<c0039e7c>] (warn_slowpath_common+0x0/0x70) from [<c0039f90>]
>> (warn_slowpath_fmt+0x38/0x40)
>>  r8:c1abfd50 r7:00000000 r6:00005000 r5:00000000 r4:80933000
>> [<c0039f58>] (warn_slowpath_fmt+0x0/0x40) from [<c0186248>]
>> (check_unmap+0x1ac/0x764)
>>  r3:c0367d55 r2:c037e24d
>> [<c018609c>] (check_unmap+0x0/0x764) from [<c0186978>]
>> (debug_dma_unmap_sg+0x100/0x134)
>> [<c0186878>] (debug_dma_unmap_sg+0x0/0x134) from [<c0019770>]
>> (dma_unmap_sg+0x24/0x7c)
>> [<c001974c>] (dma_unmap_sg+0x0/0x7c) from [<c0207220>]
>> (omap_hsmmc_post_req+0x48/0x54)
>> [<c02071d8>] (omap_hsmmc_post_req+0x0/0x54) from [<c01fb644>]
>> (mmc_start_req+0x9c/0x128)
>>  r4:c1a76000
>> [<c01fb5a8>] (mmc_start_req+0x0/0x128) from [<c02049fc>]
>> (mmc_blk_issue_rw_rq+0x80/0x460)
>>  r8:c1ab5c00 r7:00000001 r6:c1ab5824 r5:c1ab5824 r4:c1ab5c00
>> [<c020497c>] (mmc_blk_issue_rw_rq+0x0/0x460) from [<c02050a8>]
>> (mmc_blk_issue_rq+0x2cc/0x2fc)
>> [<c0204ddc>] (mmc_blk_issue_rq+0x0/0x2fc) from [<c02056c4>]
>> (mmc_queue_thread+0xa0/0x104)
>> [<c0205624>] (mmc_queue_thread+0x0/0x104) from [<c0054f8c>]
>> (kthread+0x88/0x90)
>> [<c0054f04>] (kthread+0x0/0x90) from [<c003d9a4>] (do_exit+0x0/0x618)
>>  r7:00000013 r6:c003d9a4 r5:c0054f04 r4:c1a7bc7c
>> ---[ end trace 3314ad56daf5d14f ]---
>>
>> Luckily thinks continue to work, but clearly releasing DMA mappings which
>> drivers don't own is bad news.  Unfortunately, I don't have the bandwidth
>> to be able to investigate this at present - well, I could do but then I'd
>> have to drop working on the OMAP4 vs generic suspend/resume code and learn
>> about something I've no current clue about.
>>
> Please continue your help on generic suspend.
>
>> Can someone please investigate and fix whatever is broken.
>>
> Will find somebody to look at this issue.
>
I had a look at this and my guess is that the same mapped DMA memory
is unmapped twice. First the memory is unmapped in
omap_hsmmc_dma_cleanup() due to the mmc error, then later in
omap_hsmmc_post_req(). Here is a patch to resolve that. I haven't had
the chance to test it yet though.

---
 drivers/mmc/host/omap_hsmmc.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
index 21e4a79..7f40767 100644
--- a/drivers/mmc/host/omap_hsmmc.c
+++ b/drivers/mmc/host/omap_hsmmc.c
@@ -1011,6 +1011,7 @@ static void omap_hsmmc_dma_cleanup(struct
omap_hsmmc_host *host, int errno)
                        host->data->sg_len,
                        omap_hsmmc_get_dma_dir(host, host->data));
                omap_free_dma(dma_ch);
+               data->host_cookie = 0;
        }
        host->data = NULL;
 }
@@ -1576,8 +1577,10 @@ static void omap_hsmmc_post_req(struct mmc_host
*mmc, struct mmc_request *mrq,
        struct mmc_data *data = mrq->data;

        if (host->use_dma) {
-               dma_unmap_sg(mmc_dev(host->mmc), data->sg, data->sg_len,
-                            omap_hsmmc_get_dma_dir(host, data));
+               if (data->host_cookie)
+                       dma_unmap_sg(mmc_dev(host->mmc), data->sg,
+                                    data->sg_len,
+                                    omap_hsmmc_get_dma_dir(host, data));
                data->host_cookie = 0;


I also checked the mmci code for this same issue and mmci doesn't have
the same bug.
MMCI works fine in 3.1-rc2 even though the code is "wrong". I propose
this change.
@@ -529,7 +529,7 @@ static void mmci_post_request(struct mmc_host
*mmc, struct mmc_request *mrq,
        if (chan) {
                if (err)
                        dmaengine_terminate_all(chan);
-               if (err || data->host_cookie)
+               if (data->host_cookie)

I'll post these patches as soon as I have managed to test them or
sooner if I get a tested-by.

Regards,
Per