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Received: from bhuna.collabora.co.uk ([46.235.227.227]) by bombadil.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1ldVG6-002xTG-7Z; Mon, 03 May 2021 09:53:00 +0000 Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: bbrezillon) by bhuna.collabora.co.uk (Postfix) with ESMTPSA id AC7471F4215B; Mon, 3 May 2021 10:52:55 +0100 (BST) Date: Mon, 3 May 2021 11:52:52 +0200 From: Boris Brezillon To: Pratyush Yadav Cc: , Mark Brown , Miquel Raynal , Vignesh Raghavendra , , Alexandre Torgue , , , , , Subject: Re: [PATCH 1/3] spi: spi-mem: add automatic poll status functions Message-ID: <20210503115252.08af412c@collabora.com> In-Reply-To: <20210503092935.vjitc7mc47wttn77@ti.com> References: <20210426143934.25275-1-patrice.chotard@foss.st.com> <20210426143934.25275-2-patrice.chotard@foss.st.com> <20210430185104.377d1bc6@collabora.com> <20210503084742.7cp77snyohkdwwvv@ti.com> <20210503111114.26b64e25@collabora.com> <20210503092935.vjitc7mc47wttn77@ti.com> Organization: Collabora X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210503_025258_575130_605F9D7E X-CRM114-Status: GOOD ( 57.30 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, 3 May 2021 14:59:37 +0530 Pratyush Yadav wrote: > On 03/05/21 11:11AM, Boris Brezillon wrote: > > On Mon, 3 May 2021 14:17:44 +0530 > > Pratyush Yadav wrote: > > > > > On 30/04/21 06:51PM, Boris Brezillon wrote: > > > > On Mon, 26 Apr 2021 16:39:32 +0200 > > > > wrote: > > > > > > > > > From: Christophe Kerello > > > > > > > > > > With STM32 QSPI, it is possible to poll the status register of the device. > > > > > This could be done to offload the CPU during an operation (erase or > > > > > program a SPI NAND for example). > > > > > > > > > > spi_mem_poll_status API has been added to handle this feature. > > > > > > > > > > Signed-off-by: Christophe Kerello > > > > > Signed-off-by: Patrice Chotard > > > > > --- > > > > > drivers/spi/spi-mem.c | 34 ++++++++++++++++++++++++++++++++++ > > > > > include/linux/spi/spi-mem.h | 8 ++++++++ > > > > > 2 files changed, 42 insertions(+) > > > > > > > > > > diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c > > > > > index 1513553e4080..43dce4b0efa4 100644 > > > > > --- a/drivers/spi/spi-mem.c > > > > > +++ b/drivers/spi/spi-mem.c > > > > > @@ -743,6 +743,40 @@ static inline struct spi_mem_driver *to_spi_mem_drv(struct device_driver *drv) > > > > > return container_of(drv, struct spi_mem_driver, spidrv.driver); > > > > > } > > > > > > > > > > +/** > > > > > + * spi_mem_poll_status() - Poll memory device status > > > > > + * @mem: SPI memory device > > > > > + * @op: the memory operation to execute > > > > > + * @mask: status bitmask to ckeck > > > > > + * @match: status expected value > > > > > + * @timeout: timeout > > > > > + * > > > > > + * This function send a polling status request to the controller driver > > > > > + * > > > > > + * Return: 0 in case of success, -ETIMEDOUT in case of error, > > > > > + * -EOPNOTSUPP if not supported. > > > > > + */ > > > > > +int spi_mem_poll_status(struct spi_mem *mem, > > > > > + const struct spi_mem_op *op, > > > > > + u8 mask, u8 match, u16 timeout) > > > > > +{ > > > > > + struct spi_controller *ctlr = mem->spi->controller; > > > > > + int ret = -EOPNOTSUPP; > > > > > + > > > > > + if (ctlr->mem_ops && ctlr->mem_ops->poll_status) { > > > > > + ret = spi_mem_access_start(mem); > > > > > > > > You should probably check that op is a single byte read before > > > > accepting the command. > > > > > > Please do not discriminate against 8D-8D-8D flashes ;-). > > > > Then mask and match should probably be u16 :P. And the check as it is > > seems a bit lax to me. Drivers will of course be able to reject the op > > when there's more than one byte (or 16bit word in case of 8D) to read, > > but it feels like the core could automate that a bit. > > The two 8D flashes that are currently supported in SPI NOR both have a > 1-byte status register. But to read it, the read op should be 2-byte > long to avoid partial cycles at the end. The second byte is simply > discarded. > > 2-byte wide registers might show up in the future, but for now at least > we don't have to worry about them. Well, I guess it doesn't hurt to take it into account now. I mean, what's happening on the bus in that case is a 2byte transfer, with the second byte being ignored, which you can describe with a 16bit mask of 0xMM00 (assuming big endian transfers here, as done for other ops). > > > > > > > > > > > > > > > + if (ret) > > > > > + return ret; > > > > > + > > > > > + ret = ctlr->mem_ops->poll_status(mem, op, mask, match, timeout); > > > > > > > > You also need some sort of ->poll_status_is_supported() to validate > > > > that the controller supports the status polling for this specific op (I > > > > > > I don't think a separate function is needed for checking if the poll > > > status op is supported. Return value of -EOPNOTSUPP should be able to > > > signal that. This can also be used to check if Octal DDR capable > > > controllers are able to poll using 2-byte reads. > > > > Yeah, I had something more complex in mind to avoid doing this 'try > > native mode and fall back on sw-based more if not supported' dance > > every time a status poll is requested (something similar to what we do > > for dirmaps, with a status poll desc), but I guess that's a bit > > premature (and probably uneeded). > > I think Mark also suggested something similar. Make the CPU/non-CPU case > transparent to the caller. I agree with with this direction. Makes the > caller simpler. It's kind of orthogonal to what I was suggesting, but yes, that's definitely a good idea. We certainly don't want the spi-nor layer to open code the same logic if the spi-mem layer can do it for us. > > I also mentioned in a reply to this patch that supports_op() should be > called before the op is executed. That should take care of "base" > support for the op. The poll-specific checks can go in the poll_status() > function itself. If either of those say the op is not supported, it > should fall back to CPU based polling. That's the design that makes the > most sense to me. What I had in mind was more: 1/ create a poll desc with spi_mem_create_poll_status_desc(). The "operation supported" check is done here. The controller can store all its HW-specific state in there. If the operation is not natively supported, a SW-based poll descriptor (similar to the SW-based dirmap) is created 2/ poll the status with spi_mem_poll_status(). This function is passed a poll descriptor which helps select the path that should be taken without having to check every time whether the hardware supports a specific status polling op. I can also imagine some preparation being done during the desc creation if that makes sense (preparing reg values to be written when a status poll request is issued for instance) Anyway, as I said, this sort of optimization might be a bit premature. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel