On 15 May 2012 12:10, Subhash Jadavani <subhashj@xxxxxxxxxxxxxx> wrote:
> On 5/14/2012 8:21 PM, Saugata Das wrote:
>>
>> On 14 May 2012 15:55, Subhash Jadavani<subhashj@xxxxxxxxxxxxxx> wrote:
>>>
>>> On 5/9/2012 8:18 PM, Saugata Das wrote:
>>>>
>>>> From: Saugata Das<saugata.das@xxxxxxxxxx>
>>>>
>>>> This patch adds the support for large sector size of 4KB by disabling
>>>> emulation.
>>>> This patch passes eMMC DATA_SECTOR_SIZE as the logical block size during
>>>> mmc_blk_alloc_req.
>>>>
>>>> In order to use this patch for 4KB sector size, ensure that
>>>> USE_NATIVE_SECTOR
>>>> is enabled, partition table is 4KB sector size aligned and file system
>>>> block
>>>> size is 4KB.
>>>>
>>>> Signed-off-by: Saugata Das<saugata.das@xxxxxxxxxx>
>>>> ---
>>>> drivers/mmc/card/block.c | 6 +++++-
>>>> drivers/mmc/core/mmc.c | 2 ++
>>>> 2 files changed, 7 insertions(+), 1 deletions(-)
>>>>
>>>> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
>>>> index a7c75d8..0e54118e 100644
>>>> --- a/drivers/mmc/card/block.c
>>>> +++ b/drivers/mmc/card/block.c
>>>> @@ -1517,7 +1517,11 @@ static struct mmc_blk_data
>>>> *mmc_blk_alloc_req(struct mmc_card *card,
>>>> snprintf(md->disk->disk_name, sizeof(md->disk->disk_name),
>>>> "mmcblk%d%s", md->name_idx, subname ? subname : "");
>>>>
>>>> - blk_queue_logical_block_size(md->queue.queue, 512);
>>>> + if (mmc_card_mmc(card))
>>>> + blk_queue_logical_block_size(md->queue.queue,
>>>> + card->ext_csd.data_sector_size);
>>>
>>> Shouldn't we also set the physical block size to NATIVE_SECTOR_SIZE
>>> value?
>>>
>> The physical block size gets set from blk_queue_logical_block_size
>>
>>> Other question,
>>> Did you find any eMMC device which 4K native sector size? If yes, please
>>> share the test results.
>>>
>> I have not yet seen the eMMC device implementing 4KB sector. But MMC
>> vendors are promising this feature, so I prepared this patch. So far,
>> I have tested by setting "data_sector_size" to 4KB (doing a hack in
>> mmc_read_ext_csd), configuring file system to have 4KB block size and
>> mounting it.
>
> Ok. So basically you are emulating the 512B native sector device as 4K
> native sector device and always read/write this device in 4K granularity. So
> this is just a proof of concept that setting the block queue logical sector
> size to 4K works or not?
Yes and it works. Note that, even the partition tables need to be 4KB aligned.
> Are vendors promising any performance improvement if we run the device in 4K
> sector size mode rather than emulation mode?
>
Atleast from the explanation in the spec on emulation mode, this
promises to provide some improvement. Some vendors may already have
some proprietary optimization to optimize access which are not 4KB
aligned. But lets target this 4KB alignment to have a good performance
across devices.
> I have few other doubts (from specification point of view) when the device
> starts running in native sector size mode:
>
> 1. According spec, "A large sector device shall not support partial access
> and shall not support reliable write mode EN_REL_WR=0."
> Shouldn't this patch make ensure this?
>
Yes, May be, we should add a check in mmc-util i.e. set
USE_NATIVE_SECTOR only if EN_REL_WR = 1 .
> 2. Some internal sizes reported by the device may change after successfully
> disabling of the emulation mode.
> Shouldn't we take of this as well?
>
Which parameter size will change ? I did not come across such remark
in the specification.
> 3. After a successful disabling of the emulation mode, the content of the
> User Data Area is undefined.
> If the contents of the user data area is undefined after disabling
> the emulation mode, i don't think device will be able to boot to kernel
> after power cycle. So does this mean we have to flash the kernel/file system
> images
> again? Basically i don't see a use of disabling the emulation mode
> from kernel. It should be done by basic build/image flashing utility which
> could flash the images after setting the use_native_sector field and power
> cycle.
Kernel is not disabling emulation mode. The mmc-util tool is doing it.
You are right, the flashing utility will disable the emulation mode
(mmc-util change can be used as a reference for the flashing utility).
Kernel (mmc driver) just needs to understand that the mode has changed
and notify file system accordingly (blk_queue_logical_block_size)
>
> 4. Data transfers on the bus are still using 512B CRC-protected blocks, but
> data shall only be transferred in multiple of 8 such blocks (always
> multiples of 4KB)
> So this means host controller still will be configured in 512B sector
> mode but amount of data will be in multple of 8 such 512B blocks?
>
Yes, there is no host controller change.
> 5. Sector addressing is still used, but sector addresses shall always be
> aligned to 8 (4KB)
> How the sector addressing work here? will the sector address (at
> argument of read/write commands) of byte address 0x1000 be 1 or 8?
>
> 512B sector addressing:
> (byte address) (sector address)
> 0x0000 => 0
> 0x0200 => 1
> 0x0400 => 2
> 0x0600 => 3
> 0x0800 => 4
> 0x0A00 => 5
> 0x0C00 => 6
> 0x0E00 => 7
> 0x1000 => 8
>
Yes, it continues to be 512B addressing.
> 4K sector addressing:
> (byte address) (sector address)
> 0x0000 => 0
> 0x0200 => NA
> 0x0400 => NA
> 0x0600 => NA
> 0x0800 => NA
> 0x0A00 => NA
> 0x0C00 => NA
> 0x0E00 => NA
> 0x1000 => 1
>
> 6. Arguments for read commands (CMD17/18) and write commands (CMD24/25)
> shall always be aligned to 8 (4KB)
> What will be meaning of the single block read now? Should it be use
> single 512B block or single 4KB block? If CMD17 and CMD24 now mean that
> access to 4KB memory area, don't you need to take of the same in MMC
> block driver?
Yes, single block read/write is not be allowed. From file system, we
should not have 512B read/write once we have indicated 4KB logical
sector size from blk_queue_logical_block_size.
I think we can have a check on this from mmc_blk_rw_rq_prep, where a
single block read/write request will be returned with,
__blk_end_request(req, -EIO, blk_rq_cur_bytes(req));
>
> 7. what should be the block length set by CMD16 (SET_BLOCK_LENGTH) command?
> I would guess that in 4KB native sector size mode, this command is
> redundant and will be ignored by the card but it's no where explicitly
> mentioned in specification.
>
I guess, it should be multiple of 4KB ! I see that mmc_set_blocklen is
returning the error code to the caller. So, I see nothing to be done
there.
> Regards,
> Subhash
>
>>
>>> Other than that, this patch looks good to me.
>>>
>>> Regards,
>>> Subhash
>>>
>>>> + else
>>>> + blk_queue_logical_block_size(md->queue.queue, 512);
>>>> set_capacity(md->disk, size);
>>>>
>>>> if (mmc_host_cmd23(card->host)) {
>>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>>>> index 02914d6..8dcbe995 100644
>>>> --- a/drivers/mmc/core/mmc.c
>>>> +++ b/drivers/mmc/core/mmc.c
>>>> @@ -533,6 +533,8 @@ static int mmc_read_ext_csd(struct mmc_card *card,
>>>> u8
>>>> *ext_csd)
>>>> } else {
>>>> card->ext_csd.data_tag_unit_size = 0;
>>>> }
>>>> + } else {
>>>> + card->ext_csd.data_sector_size = 512;
>>>> }
>>>>
>>>> out:
>>>
>>>
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