linux-kernel - Re: [RFC] spi: dw: support setting tmode dynamically

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Message-ID: <20160106121345.GV6588@sirena.org.uk>
Date:	Wed, 6 Jan 2016 12:13:45 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Khoa Dang Pham <kpham@....com>
Cc:	Jisheng Zhang <jszhang@...vell.com>, linux-spi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] spi: dw: support setting tmode dynamically

On Wed, Jan 06, 2016 at 08:45:38AM +0700, Khoa Dang Pham wrote:
> Hi Mark,

Please don't top post, reply in line with needed context.  This allows
readers to readily follow the flow of conversation and understand what
you are talking about and also helps ensure that everything in the
discussion is being addressed.

> According to the "DesignWare DW_apb_ssi Databook" (version 3.21b) provided
> by Synopsys, the EEPROM read is:

> "When TMOD = 2‘b11, the transmit data is used to transmit an opcode and/or
> an address to the EEPROM
> device. Typically this takes three data frames (8-bit opcode followed by
> 8-bit upper address and 8-bit lower
> address). During the transmission of the opcode and address, no data is
> captured by the receive logic (as
> long as the DW_apb_ssi master is transmitting data on its txd line, data on
> the rxd line is ignored). The

This is just a normal data transfer, if the driver is functioning
correctly this should not be required and requiring it would mean that
we'd need to go round adding workarounds for this to lots of client
drivers.  It seems like you are trying to work around some other bug in
the driver, quite possibly incorrect handling of chip select as was
suggested elsewhere.  If that is the case a common solution is to manage
the chip select as a GPIO rather than with the built in handling in the
block if the block can't cope.

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