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). > And there is no > info indicating capabilities of spi-master wrt no of IO lines for > opcode/address/data that it can support. For a true SPI controller, there is no need to specify something different for opcode/address/data, since all those are treated the same; they're just bits on 1, 2, or 4 lines. So the SPI_{TX,RX}_{DUAL,QUAD} mode flags in struct spi_master tell m25p80 all it needs to know. > > There are typically both flash device and SPI controller constraints > > on this question, so there needs to be some kind of negotiation > > involved, I expect. Or at least, the SPI master needs to expose which > > modes it can support with this flash-read API. > > > > If spi-master capabilities are known For generic SPI handling, these are already known. But now you're adding flash-specific capabilities, and I'm not going to assume that all accelerated-read (e.g., your TI mmap'ed flash read) support all the same modes as your generic modes. So, which modes does your mmap'ed read handle? 1/1/1? 1/1/2? 1/1/4? 4/4/4? (where x/y/z means x lines for opcode, y lines for address, and z lines for data) > then spi_mmap_read_supported() (or > a new function perhaps) can be used for negotiation. These capabilities > can be added incrementally once ability to specify spi-master > capabilities are in place. spi_master capabilities are already in place. So now you need to describe them for your new interface too. > > Also, this API doesn't actually have anything to do with memory mapping. > > It has to do with the de facto standard flash protocol. So I don't think > > mmap belongs in the name; it should be something about flash. (I know of > > at least one other controller that could probably use this API, excpet > > it doesn't use memory mapping to accomplish the accelerated flash read.) > > > > As far as TI QSPI controller is concerned, the accelerated read happens > via mmap port whereby a predefined memory address space of SoC is > exposed as QSPI mmap region. This region can be accessed like normal > RAM(via memcpy()) and the QSPI controller interface takes care of > fetching data from flash on SPI bus automatically I understand all that, but the API as it currently stands is not tied to that implementation at all. > hence, I named it as > above. But, I have no hard feelings if it needs to be generalized to > spi_mtd_read() or something else. Maybe spi_flash_read()? It's technically not limited to MTD, though it probably would only be used there. (And please, don't tread on the 'spi_nor_' prefix, as we already have a related, but distinct, framework using that.) Brian -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html