Re: [PATCH v3 1/5] spi: introduce mmap read support for spi flash devices

[Cyrille Pitchen <cyrille.pitchen@xxxxxxxxx>]

Hi Brian,

Le 11/11/2015 08:20, Brian Norris a écrit :
> Hi,
> 
> On Wed, Nov 11, 2015 at 12:20:46PM +0530, R, Vignesh wrote:
>> On 11/11/2015 4:53 AM, Brian Norris wrote:
>>> On Tue, Nov 10, 2015 at 10:59:55AM +0530, Vignesh R wrote:
>>>> diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
>>>> index cce80e6dc7d1..2f2c431b8917 100644Hi
>>>> --- a/include/linux/spi/spi.h
>>>> +++ b/include/linux/spi/spi.h
>>>> @@ -361,6 +361,11 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
>>>>   * @handle_err: the subsystem calls the driver to handle an error that occurs
>>>>   *		in the generic implementation of transfer_one_message().
>>>>   * @unprepare_message: undo any work done by prepare_message().
>>>> + * @spi_mtd_mmap_read: some spi-controller hardwares provide memory.
>>>> + *                     Flash drivers (like m25p80) can request memory
>>>> + *                     mapped read via this method. This interface
>>>> + *                     should only be used by mtd flashes and cannot be
>>>> + *                     used by other spi devices.
>>>>   * @cs_gpios: Array of GPIOs to use as chip select lines; one per CS
>>>>   *	number. Any individual value may be -ENOENT for CS lines that
>>>>   *	are not GPIOs (driven by the SPI controller itself).
>>>> @@ -507,6 +512,11 @@ struct spi_master {
>>>>  			       struct spi_message *message);
>>>>  	int (*unprepare_message)(struct spi_master *master,
>>>>  				 struct spi_message *message);
>>>> +	int (*spi_mtd_mmap_read)(struct  spi_device *spi,
>>>> +				 loff_t from, size_t len,
>>>> +				 size_t *retlen, u_char *buf,
>>>> +				 u8 read_opcode, u8 addr_width,
>>>> +				 u8 dummy_bytes);
>>>
>>> Is this API really sufficient? There are actually quite a few other
>>> flash-related parameters that might be relevant to a controller. I
>>> presume you happen not hit them because of the particular cases you're
>>> using this for right now, but:
>>>
>>>  * How many I/O lines are being used? These can vary depending on the
>>>    type of flash and the number of I/O lines supported by the controller
>>>    and connected on the board.
>>>
>>
>> This API communicates whatever data is currently communicated via
>> spi_message through spi_sync/transfer_one interfaces.
> 
> No it doesn't. A spi_message consists of a list of spi_transfer's, and
> each spi_transfer has tx_nbits and rx_nbits fields.
> 
>>>  * The previous point can vary across parts of the message. There are
>>>    various combinations of 1/2/4 lines used for opcode/address/data. We
>>>    only support a few of those combinations in m25p80 right now, but
>>>    you're not specifying any of that in this API. I guess you're just
>>>    making assumptions? (BTW, I think there are others having problems
>>>    with the difference between different "quad" modes on Micron flash; I
>>>    haven't sorted through all the discussion there.)
>>>
>>
>> How is the spi controller currently being made aware of this via
>> m25p80_read / spi_sync() interface? AFAIK, mode field of spi_device
>> struct tell whether to do normal/dual/quad read but there is no info
>> communicated wrt 1/2/4 opcode/address/data combinations.
> 
> Yes there is. m25p80 fills out spi_transfer::rx_nbits. Currently, we
> only use this for the data portion, but it's possible to support more
> lines for the address and opcode portions too, using the rx_nbits for
> the opcode and address spi_transfer struct(s) (currently, m25p80_read()
> uses 2 spi_transfers per message, where the first one contains opcode +
> address + dummy on a single line, and the second transfer receives the
> data on 1, 2, or 4 lines).
> 

In September I've sent a series of patches to enhance the support of QSPI flash
memories. Patch 4 was dedicated to the m25p80 driver and set the
rx_nbits / tx_nbits fields of spi_transfer struct(s) in order to configure the
number of I/O lines independently for the opcode, address and data parts.
The work was done for m25p80_read() but also for _read_reg(), _write_reg() and
_write().
The patched m25p80 driver was then tested with an at25 memory to check non-
regression.

This series of patches also added 4 enum spi_protocol fields inside struct
spi_nor so the spi-nor framework can tell the (Q)SPI controller driver what SPI
protocol should be use for erase, read, write and register read/write
operations, depending on the memory manufacturer and the command opcode.
This was done to better support Micron, Spansion and Macronix QSPI memories.

I have tested the series with Micron QSPI memories and Atmel QSPI controller
and I guess Marek also tested it on his side with Spansion QSPI memories and
another QSPI controller.

So if it can help other developers to develop QSPI controller drivers, the
series is still available there:

for the whole series:
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-September/371170.html

for patch 4 (depends on patch 2 for enum spi_protocol):
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-September/371173.html

Best Regards,

Cyrille
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