Messages in this thread | | | Date | Thu, 14 May 2015 11:36:57 -0700 | From | Scott Branden <> | Subject | Re: [PATCH 2/2] spi: bcm-mspi: Add support for Broadcom MSPI driver. |
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On 15-05-14 11:28 AM, Florian Fainelli wrote: > On 14/05/15 11:19, Scott Branden wrote: >> Hi Mark, >> >> On 15-05-14 03:31 AM, Mark Brown wrote: >>> On Wed, May 13, 2015 at 05:19:06PM -0700, Scott Branden wrote: >>> >>>> The purpose of this mspi interface is to connect to NOR flash. There >>>> are >>>> other SPI interfaces on the devices used to connect to other SPI >>>> devies. We >>>> don't have any need to support full duplex slaves on this port (NOR >>>> have any >>>> hardware wired this way - pun realized after typing this). >>> >>> Chip vendors often say this sort of thing and then get surprised by what >>> their users choose to do, and even if it only ever gets used with flash >>> all it would take is some new flash command which can use full duplex >>> for something. Please write the code so it at least tries to handle >>> full duplex operation, if you can't test it fully that's not the end of >>> the world. It doesn't look like it should be particularly difficult. >>> >> Yes, there is always room for improvements in code. In this case - it >> really is not worth our time to add code we can't test. We try to >> deliver code that we can test and actually works. Yes, if anyone needs >> to use the mspi for full duplex operation code can be added in the >> future - it is software. This block has gone through many generations >> of our SoCs and has only been used for this purpose - the bootROM boots >> from this SPI only. It is dedicated for this purpose. >> >> Also, there are other SPI blocks on the SoC that are used for connect >> other SPI devices. These SPI blocks are properly designed for >> full-duplex operation. This mspi block is designed for connecting to >> NOR flash. > > This is an implementation detail and architectural choice that is > specific to the Cygnus SoCs where a single MSPI is present, right? > > This same MSPI block is instantiated multiple times in BCM7xxx chips to > interface to general purpose SPI slaves, ranging from Ethernet switches > to bluetooth chips etc... those will definitively want full-duplex to be > working. > > I would greatly appreciate if some thought to supporting full duplex > transfers was given in this driver drop. If you cannot test that, then > maybe just flag the driver has been half-duplex only for now... > > Thank you. > Hi Florian, Yes, we can flag that - but we have no understanding of how the block operates in this mode. It would be great if your team could add the necessary full duplex support in a patch enhancement to the driver?
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