On 15 May 2012 15:47, S, Venkatraman <svenkatr@xxxxxx> wrote:
> On Tue, May 15, 2012 at 12:10 PM, 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?
>> Are vendors promising any performance improvement if we run the device in 4K
>> sector size mode rather than emulation mode?
>>
>> 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?
>>
>> 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?
> This would be because if a single 512byte sector was marked as bad
> (unusable) initially, the entire
> aligned 4K block would be marked as bad now after switching to 4K
> sector size, resulting in a slight capacity shrinkage.
> This would only matter if the switch happens for a fairly old
> device. Typically, the sector size change should happen during factory
> initialization, so there wouldn't be too many bad blocks, so it
> shouldn't be much of an issue now.
> Of course, this is just one aspect of a problem for the "dynamic
> device capacity" feature of eMMC4.5, and can be solved if we get to
> that..
>
If 512byte sector becomes bad, then the complete NAND block (much
larger than 4KB) will be marked bad. As such, there should be no
difference in terms of amount of shrinkage. But yes, we need to start
thinking about "dynamic device capacity" once the number of bad NAND
blocks exceeds what eMMC can afford.
>
>>
>> 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.
>>
>> 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?
>>
>> 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
>>
>> 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?
>>
>> 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.
>>
>> 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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>>
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