Re: [PATCH linux-next v3 1/1] spi: imx: dynamic burst length adjust for PIO mode

[Jiada Wang]

On 06/01/2017 10:38 PM, Sascha Hauer wrote:
> On Thu, Jun 01, 2017 at 04:58:47AM -0700, Jiada Wang wrote:
> > Hi Sascha
> >
> > On 05/29/2017 02:50 AM, Sascha Hauer wrote:
> > > Hi,
> > >
> > > On Thu, May 25, 2017 at 10:02:42PM -0700, jiada_wang@xxxxxxxxxx wrote:
> > > > From: Jiada Wang<jiada_wang@xxxxxxxxxx>
> > > >
> > > > previously burst length (BURST_LENGTH) is always set to equal
> > > > to bits_per_word, causes a 10us gap between each word in
> > > > transfer, which significantly affects performance.
> > > >
> > > > This patch uses 32 bits transfer to simulate lower bits transfer,
> > > > and adjusts burst length runtimely to use biggeest burst length
> > > > as possible to reduce the gaps in transfer for PIO mode.
> > > First let me say that I'm not really looking forward to have this patch
> > > in the driver. It adds quite some code to already hairy code pathes in
> > > the imx-spi driver and I saw you have the same patch for DMA mode
> > > aswell.
> > >
> > > The driver has different function hooks for the different controllers.
> > > This patch breaks that. In some places it assumes that dynamic burst
> > > is only possible on i.MX51 type controllers and also that in case
> > > dynamic burst is enabled it must be an i.MX51 type controller.
> > >
> > > We should really see how this patch can be better integrated into the
> > > driver, or, how the driver can be changed to better support the dynamic
> > > burst usecase.
> >   Yes, I can understand your concern, as this patch brings in a bunch of
> > change,
> > and changes the behaviour of data transfer.
> > how about introduce a new DTS property like "fsl,spi-dynamic-burst",
> > and only enables dynamic burst when this property is added.
> This will only reduce the testing coverage of the feature, not a good
> option.
As an improvement, I am thinking about the following
1. introduce a 'fsl,spi-dynamic-burst' property in dts as mentioned before
2. remove all change in specific functions hooks, for example 
"mx51_ecspi_config"
3. introduce spi_imx_pio_dynamic_burst_transfer(), which will handle 
actual swapped data transfer,
    and burst length adjustment.


What do you think ?
> Sascha