From: Alexander Stein <alexander.stein@systec-electronic.com>
To: bhuvanchandra.dv@toradex.com
Cc: linux-kernel@vger.kernel.org, broonie@kernel.org, stefan@agner.ch,
        linux-spi@vger.kernel.org
Subject: Re: [PATCH v2] spi-fsl-dspi: Fix CTAR Register access
Date: Thu, 10 Dec 2015 10:06:11 +0100
Message-ID: <120830674.SMntmZQuCR@ws-stein>
User-Agent: KMail/4.14.8 (Linux/4.1.12-gentoo; KDE/4.14.8; x86_64; ; )
In-Reply-To: <56693B5B.6060100@toradex.com>
References: <1449726930-7378-1-git-send-email-bhuvanchandra.dv@toradex.com> <2295258.Vc5Dp4nsCT@ws-stein> <56693B5B.6060100@toradex.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2492
Lines: 54

On Thursday 10 December 2015 14:14:11, Bhuvanchandra DV wrote:
> On 12/10/2015 12:45 PM, Alexander Stein wrote:
> > On Thursday 10 December 2015 11:25:30, Bhuvanchandra DV wrote:
> >> DSPI instances in Vybrid have a different amount of chip selects
> >> and CTARs (Clock and transfer Attributes Register). In case of
> >> DSPI1 we only have 2 CTAR registers and 4 CS. In present driver
> >> implementation CTAR offset is derived from CS instance which will
> >> lead to out of bound access if chip select instance is greater than
> >> CTAR register instance, hence use single CTAR0 register for all CS
> >> instances. Since we write the CTAR register anyway before each access,
> >> there is no value in using the additional CTAR registers. Also one
> >> should not program a value in CTAS for a CTAR register that is not
> >> present, hence configure CTAS to use CTAR0.
> >
> > Shouldn't the information put into struct fsl_dspi_devtype_data how much CTAR and CS the actual implementation has available? E.g. LS1021A has 6 CS and 4 CTAR
> 
> I guess still this will not help us when CS instance greater than CTAR 
> instance is selected. Other point to consider here is we are writing the 
> CTAR register before every access, so for us there is no additional 
> advantage of using multiple CTAR registers.

Please have a look at 5cc7b04740effa5cc0af53f434134b5859d58b73 which addresses this problem for the 4 CTAR and 6 CS case.
I'm unsure how multiple CTAR will help at all. But at the end the amount of CS seems to be different for different implementations. So this still needs to be added to fsl_dspi_devtype_data.

Best regards,
Alexander
-- 
-----
Please note our closure period for Christmas vacation and turn of the year
We are closed from 21st December 2015 to 3rd January 2016
-----
Dipl.-Inf. Alexander Stein
SYS TEC electronic GmbH
alexander.stein@systec-electronic.com

Legal and Commercial Address:
Am Windrad 2
08468 Heinsdorfergrund
Germany

Office: +49 (0) 3765 38600-0
Fax:    +49 (0) 3765 38600-4100
 
Managing Directors:
	Director Technology/CEO: Dipl.-Phys. Siegmar Schmidt;
	Director Commercial Affairs/COO: Dipl. Ing. (FH) Armin von Collrepp
Commercial Registry:
	Amtsgericht Chemnitz, HRB 28082; USt.-Id Nr. DE150534010

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/