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Date: Wed, 7 Dec 2016 17:32:45 +0100
From: Marek Vasut <marek.vasut@...il.com>
To: Cyrille Pitchen <cyrille.pitchen@...el.com>
Cc: computersforpeace@...il.com, boris.brezillon@...e-electrons.com,
richard@....at, linux-mtd@...ts.infradead.org,
linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
broonie@...nel.org
Subject: Re: [PATCH 2/2] mtd: spi-nor: add a stateless method to support
memory size above 128Mib
On 12/07/2016 05:29 PM, Cyrille Pitchen wrote:
> Le 07/12/2016 à 17:20, Marek Vasut a écrit :
>> On 12/06/2016 05:52 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/spi-nor/spi-nor.c | 114 ++++++++++++++++++++++++++++++++++--------
>>> 1 file changed, 93 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
>>> index 8abe134e174a..606c030c566d 100644
>>> --- a/drivers/mtd/spi-nor/spi-nor.c
>>> +++ b/drivers/mtd/spi-nor/spi-nor.c
>>> @@ -75,6 +75,10 @@ struct flash_info {
>>> * bit. Must be used with
>>> * SPI_NOR_HAS_LOCK.
>>> */
>>> +#define SPI_NOR_4B_OPCODES BIT(10) /*
>>> + * Use dedicated 4byte address op codes
>>> + * to support memory size above 128Mib.
>>> + */
>>> };
>>>
>>> #define JEDEC_MFR(info) ((info)->id[0])
>>> @@ -188,6 +192,91 @@ static inline struct spi_nor *mtd_to_spi_nor(struct mtd_info *mtd)
>>> return mtd->priv;
>>> }
>>>
>>> +
>>> +struct spi_nor_address_entry {
>>> + u8 src_opcode;
>>> + u8 dst_opcode;
>>> +};
>>> +
>>> +static u8 spi_nor_convert_opcode(u8 opcode,
>>> + const struct spi_nor_address_entry *entries,
>>> + size_t num_entries)
>>> +{
>>> + int min, max;
>>> +
>>> + /*
>>> + * This function implements a dichotomic search in the entries[]
>>> + * array indexed by src_opcode. Hence we assume that the entries[]
>>> + * array is sorted by src_opcode.
>>> + * The dichotomic search has a logarithmic complexity as opposed
>>> + * to a simple loop on all entires, which has a linear complexity:
>>> + * it means that when n is the number of entries in the input array,
>>> + * the dichotomic search performs O(log2(n)) comparisons whereas
>>> + * a simple loop performs O(n) comparisons.
>>> + */
>>> + min = 0;
>>> + max = num_entries - 1;
>>> + while (min <= max) {
>>> + 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;
>>> + }
>>
>> You have like 16 entries in that table, just do a linear search, this is
>> only complex for no benefit.
>
> Well ok, I agree with you, it's too much overkill for what it does.
> For readiness purpose, what about a simple and straight forward switch()
> statement? Let's forget about cache-line and other memory/time optimizations :)
If you do a switch, you cannot walk a table which you pass in, see below.
>>> + /* No conversion found */
>>> + return opcode;
>>> +}
>>> +
>>> +static u8 spi_nor_3to4_opcode(u8 opcode)
>>> +{
>>> + /* MUST be sorted by 3byte opcode (cf spi_nor_convert_opcode). */
>>> +#define ENTRY_3TO4(_opcode) { _opcode, _opcode##_4B }
>>> + static const struct spi_nor_address_entry spi_nor_3to4_table[] = {
>>
>> You can make this static const struct const for extra constness :-)
>>
>>> + 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 */
>>
>> I'd probably break this into three smaller tables, read/program/erase
>> and then call something like:
>>
>> spi_nor_3to4_opcode(nor->read_opcode, read_opcode_table,
>> ARRAY_SIZE(read_opcode_table));
>>
>> This would further reduce the table size (heck, it'd probably fit into a
>> cacheline), so linear search would be more than enough.
>>
>>> + };
>>> +#undef ENTRY_3TO4
>>> +
>>> + return spi_nor_convert_opcode(opcode, spi_nor_3to4_table,
>>> + ARRAY_SIZE(spi_nor_3to4_table));
>>> +}
>>> +
>>> +static void spi_nor_set_4byte_opcodes(struct spi_nor *nor,
>>> + const struct flash_info *info)
>>> +{
>>> + /* Do some manufacturer fixups first */
>>> + switch (JEDEC_MFR(info)) {
>>> + case SNOR_MFR_SPANSION:
>>> + /* No small sector erase for 4-byte command set */
>>> + nor->erase_opcode = SPINOR_OP_SE;
>>> + nor->mtd.erasesize = info->sector_size;
>>> + break;
>>> +
>>> + default:
>>> + break;
>>> + }
>>> +
>>> + nor->read_opcode = spi_nor_3to4_opcode(nor->read_opcode);
>>> + nor->program_opcode = spi_nor_3to4_opcode(nor->program_opcode);
>>> + nor->erase_opcode = spi_nor_3to4_opcode(nor->erase_opcode);
>>> +}
>>> +
>>> /* Enable/disable 4-byte addressing mode. */
>>> static inline int set_4byte(struct spi_nor *nor, const struct flash_info *info,
>>> int enable)
>>> @@ -1486,27 +1575,10 @@ int spi_nor_scan(struct spi_nor *nor, const char *name, enum read_mode mode)
>>> else if (mtd->size > 0x1000000) {
>>> /* enable 4-byte addressing if the device exceeds 16MiB */
>>> nor->addr_width = 4;
>>> - if (JEDEC_MFR(info) == SNOR_MFR_SPANSION) {
>>> - /* Dedicated 4-byte command set */
>>> - switch (nor->flash_read) {
>>> - case SPI_NOR_QUAD:
>>> - nor->read_opcode = SPINOR_OP_READ_1_1_4_4B;
>>> - break;
>>> - case SPI_NOR_DUAL:
>>> - nor->read_opcode = SPINOR_OP_READ_1_1_2_4B;
>>> - break;
>>> - case SPI_NOR_FAST:
>>> - nor->read_opcode = SPINOR_OP_READ_FAST_4B;
>>> - break;
>>> - case SPI_NOR_NORMAL:
>>> - nor->read_opcode = SPINOR_OP_READ_4B;
>>> - break;
>>> - }
>>> - nor->program_opcode = SPINOR_OP_PP_4B;
>>> - /* No small sector erase for 4-byte command set */
>>> - nor->erase_opcode = SPINOR_OP_SE_4B;
>>> - mtd->erasesize = info->sector_size;
>>> - } else
>>> + if (JEDEC_MFR(info) == SNOR_MFR_SPANSION ||
>>> + info->flags & SPI_NOR_4B_OPCODES)
>>> + spi_nor_set_4byte_opcodes(nor, info);
>>> + else
>>> set_4byte(nor, info, 1);
>>> } else {
>>> nor->addr_width = 3;
>>>
>>
>>
>
--
Best regards,
Marek Vasut
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