Re: [PATCH 00/16] mtd: spi-nor: aspeed: AST2600 support and extensions

["Cédric Le Goater" <clg@kaod.org>]

On 11/10/2019 08:45, Boris Brezillon wrote:
> On Thu, 10 Oct 2019 23:47:45 +0000
> Joel Stanley <joel@jms.id.au> wrote:
> 
>> On Wed, 9 Oct 2019 at 20:56, Boris Brezillon
>> <boris.brezillon@collabora.com> wrote:
>>>
>>> Hi Cedric,
>>>
>>> On Fri,  4 Oct 2019 13:59:03 +0200
>>> Cédric Le Goater <clg@kaod.org> wrote:
>>>  
>>>> Hello,
>>>>
>>>> This series first extends the support for the Aspeed AST2500 and
>>>> AST2400 SMC driver. It adds Dual Data support and read training giving
>>>> the best read settings for a given chip. Support for the new AST2600
>>>> SoC is added at the end.
>>>>
>>>> I understand that a new spi_mem framework exists and I do have an
>>>> experimental driver using it. But unfortunately, it is difficult to
>>>> integrate the read training. The Aspeed constraints are not compatible
>>>> and i haven't had the time to extend the current framework.  
>>>
>>> Hm, I don't think that's a good reason to push new features to the
>>> existing driver, especially since I asked others to migrate their
>>> drivers to spi-mem in the past. I do understand your concerns, and I'll
>>> let the SPI NOR/MTD maintainers make the final call, but I think it'd
>>> be better for the SPI MEM ecosystem to think about this link-training
>>> API (Vignesh needs it for the Cadence driver IIRC) rather than pushing
>>> this kind of feature to spi-nor controller drivers.  
>>
>> As Cedric mentioned, the OpenBMC project has been shipping the read
>> training code for the ast2400/ast2400 for several years now. It would
>> be great to see it in mainline.
>>
>> I think it's reasonable to ask for the driver to be moved to the
>> spi-mem subsystem once it has the required APIs.
> 
> Except it won't have the necessary APIs unless someone works on it, and
> adding this feature to existing spi-nor drivers won't help achieving
> this goal.


What would you suggest ? Something like the patch below which would
call a 'train' operation at the end of spi_add_device().

Also, when doing read training, we might need to know some lowlevel 
characteristics of the chip being trained. Should we offer a way 
to grab the probed m25p80 device and give access to the underlying 
'struct spi_nor' ? 

  static struct spi_nor *spi_get_pnor(struct spi_device *spi)
  {
	struct spi_mem *spimem = spi_get_drvdata(spi);
	struct m25p *flash = spi_mem_get_drvdata(spimem);

	return flash ? &flash->spi_nor : NULL;
  }

Yeah, it's hideous. I just want to raise the issue.

Thanks,

C. 


From b34297e6b991ff051bc1e16103d14b2a05c81827 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= <clg@kaod.org>
Date: Fri, 11 Oct 2019 11:09:33 +0200
Subject: [PATCH] spi: core: Add a device link training operation
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 include/linux/spi/spi.h |  4 ++++
 drivers/spi/spi.c       | 23 +++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index af4f265d0f67..950b39304807 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -409,6 +409,7 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
  * @fw_translate_cs: If the boot firmware uses different numbering scheme
  *	what Linux expects, this optional hook can be used to translate
  *	between the two.
+ * @train : perform device link training
  *
  * Each SPI controller can communicate with one or more @spi_device
  * children.  These make a small bus, sharing MOSI, MISO and SCK signals
@@ -604,6 +605,9 @@ struct spi_controller {
 	void			*dummy_tx;
 
 	int (*fw_translate_cs)(struct spi_controller *ctlr, unsigned cs);
+
+	int			(*train)(struct spi_device *spi);
+
 };
 
 static inline void *spi_controller_get_devdata(struct spi_controller *ctlr)
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 75ac046cae52..759a66d74822 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -542,6 +542,22 @@ static int spi_dev_check(struct device *dev, void *data)
 	return 0;
 }
 
+/**
+ * spi_train - link training of SPI device
+ * @spi: the device whose being trained
+ *
+ * Return: zero on success, else a negative error code.
+ */
+static int spi_train(struct spi_device *spi)
+{
+	int		status = 0;
+
+	if (spi->controller->train)
+		status = spi->controller->train(spi);
+
+	return status;
+}
+
 /**
  * spi_add_device - Add spi_device allocated with spi_alloc_device
  * @spi: spi_device to register
@@ -606,6 +622,13 @@ int spi_add_device(struct spi_device *spi)
 	else
 		dev_dbg(dev, "registered child %s\n", dev_name(&spi->dev));
 
+	status = spi_train(spi);
+	if (status < 0) {
+		dev_err(dev, "can't train %s, status %d\n",
+				dev_name(&spi->dev), status);
+		goto done;
+	}
+
 done:
 	mutex_unlock(&spi_add_lock);
 	return status;
-- 
2.21.0



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