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Date: Tue, 25 Oct 2016 16:53:02 +0200
From: Marek Vasut <marex@...x.de>
To: Cyrille Pitchen <cyrille.pitchen@...el.com>,
computersforpeace@...il.com, linux-mtd@...ts.infradead.org
Cc: nicolas.ferre@...el.com, boris.brezillon@...e-electrons.com,
richard@....at, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/9] mtd: spi-nor: add an alternative method to support
memory >16MiB
On 10/25/2016 11:18 AM, Cyrille Pitchen wrote:
> Le 25/10/2016 à 00:10, Marek Vasut a écrit :
>> On 10/24/2016 06:34 PM, Cyrille Pitchen wrote:
>>> This patch provides an alternative mean to support memory above 16MiB
>>> (128Mib) by replacing 3byte address op codes by their associated 4byte
>>> address versions.
>>>
>>> Using the dedicated 4byte address op codes doesn't change the internal
>>> state of the SPI NOR memory as opposed to using other means such as
>>> updating a Base Address Register (BAR) and sending command to enter/leave
>>> the 4byte mode.
>>>
>>> Hence when a CPU reset occurs, early bootloaders don't need to be aware
>>> of BAR value or 4byte mode being enabled: they can still access the first
>>> 16MiB of the SPI NOR memory using the regular 3byte address op codes.
>>>
>>> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...el.com>
>>> Tested-by: Vignesh R <vigneshr@...com>
>>> ---
>>> drivers/mtd/devices/serial_flash_cmds.h | 7 ---
>>> drivers/mtd/devices/st_spi_fsm.c | 28 ++++-----
>>> drivers/mtd/spi-nor/spi-nor.c | 104 +++++++++++++++++++++++++-------
>>> include/linux/mtd/spi-nor.h | 22 +++++--
>>> 4 files changed, 113 insertions(+), 48 deletions(-)
>>>
>>> diff --git a/drivers/mtd/devices/serial_flash_cmds.h b/drivers/mtd/devices/serial_flash_cmds.h
>>> index f59a125295d0..8b81e15105dd 100644
>>> --- a/drivers/mtd/devices/serial_flash_cmds.h
>>> +++ b/drivers/mtd/devices/serial_flash_cmds.h
>>> @@ -18,19 +18,12 @@
>>> #define SPINOR_OP_RDVCR 0x85
>>>
>>> /* JEDEC Standard - Serial Flash Discoverable Parmeters (SFDP) Commands */
>>> -#define SPINOR_OP_READ_1_2_2 0xbb /* DUAL I/O READ */
>>> -#define SPINOR_OP_READ_1_4_4 0xeb /* QUAD I/O READ */
>>> -
>>> #define SPINOR_OP_WRITE 0x02 /* PAGE PROGRAM */
>>> #define SPINOR_OP_WRITE_1_1_2 0xa2 /* DUAL INPUT PROGRAM */
>>> #define SPINOR_OP_WRITE_1_2_2 0xd2 /* DUAL INPUT EXT PROGRAM */
>>> #define SPINOR_OP_WRITE_1_1_4 0x32 /* QUAD INPUT PROGRAM */
>>> #define SPINOR_OP_WRITE_1_4_4 0x12 /* QUAD INPUT EXT PROGRAM */
>>>
>>> -/* READ commands with 32-bit addressing */
>>> -#define SPINOR_OP_READ4_1_2_2 0xbc
>>> -#define SPINOR_OP_READ4_1_4_4 0xec
>>> -
>>
>> It'd be nice to have this move/rename bit factored out into a separate
>> patch.
>>
>
> OK, I will try to do this. Anyway, this rename seems to break the freshly
> merged drivers/spi/spi-bcm-qspi.c, which uses the SPINOR_OP_READ4_* macro so
> I have to do something about this driver. IMHO, the broadcom driver should not
> select its own op code but use the one provided by read_opcode member of the
> struct spi_flash_read_message.
Thanks
>>> /* Configuration flags */
>>> #define FLASH_FLAG_SINGLE 0x000000ff
>>> #define FLASH_FLAG_READ_WRITE 0x00000001
>>> diff --git a/drivers/mtd/devices/st_spi_fsm.c b/drivers/mtd/devices/st_spi_fsm.c
>>> index 5454b4113589..804313a33f2b 100644
>>
>> [...]
>>
>>> +static u8 spi_nor_convert_opcode(u8 opcode,
>>> + const struct spi_nor_address_entry *entries,
>>> + size_t num_entries)
>>> +{
>>> + int min, max;
>>> +
>>> + min = 0;
>>> + max = num_entries - 1;
>>> + while (min <= max) {
>>
>> It's really not clear at all what this function does, so please add a
>> comment.
>>
>
> This is just a dichotomic search to reduce the number of comparisons: it
> assumes the entries[] array is sorted by ascending src_opcode.
>
> I will add a comment to clarify this point.
Cool, that'd help. Are you invoking this every time an opcode is
submitted to the SPI NOR ?
>>> + int mid = (min + max) >> 1;
>>> + const struct spi_nor_address_entry *entry = &entries[mid];
>>> +
>>> + if (opcode == entry->src_opcode)
>>> + return entry->dst_opcode;
>>> +
>>> + if (opcode < entry->src_opcode)
>>> + max = mid - 1;
>>> + else
>>> + min = mid + 1;
>>> + }
>>> +
>>> + /* No conversion found */
>>> + return opcode;
>>> +}
>>> +
>>> +static u8 spi_nor_3to4_opcode(u8 opcode)
>>> +{
>>> + /* MUST be sorted by 3byte opcode */
>>
>> Because ... why ?
>>
>
> As explained above, the dichotomic search implemented in
> spi_nor_convert_opcode() assumes that the input array is sorted by src_opcode.
Maybe you should drop that assumption and do normal traversal of the
array ? I feel this is a bit fragile and will break once someone will
cluelessly add a new opcode.
... or add a comment with a big WARNING statement.
>>> +#define ENTRY_3TO4(_opcode) { _opcode, _opcode##_4B }
>>
>> Will this break/be unflexible for flashes with some different 4B opcodes ?
>>
>
> Of course I cannot provide any guarantee that it will never happen but
> currently it seems that all manufacturers use the same op codes. Besides,
> the 4-byte address instruction set is part the of JESD216B specification,
> so there is a standard for these op codes and new SPI NOR memories tend
> to match this specification by providing the SFDP tables.
Great. Still, will the code need an overhaul if some vendor decides to
deviate ?
> Indeed this instruction set is maybe one of the few things where all
> manufacturers seem to agree :)
That's a good start :)
>>> + static const struct spi_nor_address_entry spi_nor_3to4_table[] = {
>>> + ENTRY_3TO4(SPINOR_OP_PP), /* 0x02 */
>>> + ENTRY_3TO4(SPINOR_OP_READ), /* 0x03 */
>>> + ENTRY_3TO4(SPINOR_OP_READ_FAST), /* 0x0b */
>>> + ENTRY_3TO4(SPINOR_OP_BE_4K), /* 0x20 */
>>> + ENTRY_3TO4(SPINOR_OP_PP_1_1_4), /* 0x32 */
>>> + ENTRY_3TO4(SPINOR_OP_PP_1_4_4), /* 0x38 */
>>> + ENTRY_3TO4(SPINOR_OP_READ_1_1_2), /* 0x3b */
>>> + ENTRY_3TO4(SPINOR_OP_BE_32K), /* 0x52 */
>>> + ENTRY_3TO4(SPINOR_OP_READ_1_1_4), /* 0x6b */
>>> + ENTRY_3TO4(SPINOR_OP_READ_1_2_2), /* 0xbb */
>>> + ENTRY_3TO4(SPINOR_OP_SE), /* 0xd8 */
>>> + ENTRY_3TO4(SPINOR_OP_READ_1_4_4), /* 0xeb */
>>> + };
>>> +#undef ENTRY_3TO4
>>> +
>>> + return spi_nor_convert_opcode(opcode, spi_nor_3to4_table,
>>> + ARRAY_SIZE(spi_nor_3to4_table));
>>> +}
>>> +
>>
>> [...]
>>
>
--
Best regards,
Marek Vasut
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