From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Neuendorffer Subject: RE: Device tree BSP Date: Sun, 5 Jul 2009 13:43:47 -0700 Message-ID: <20090705204647.1BBCAB2004B@mail107-dub.bigfish.com> References: <4A49F472.3030902@petalogix.com><20090704181837.4DC219B0051@mail75-va3.bigfish.com> <1d3f23370907050218l6b2eb9emdbcb7dc321dbab5a@mail.gmail.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1129750363==" Return-path: Content-Class: urn:content-classes:message List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Mime-version: 1.0 Sender: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-mnsaURCQ41sdnm+yROfE0A@public.gmane.org Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-mnsaURCQ41sdnm+yROfE0A@public.gmane.org To: John Williams Cc: John Linn , michal.simek-g5w7nrANp4BDPfheJLI6IQ@public.gmane.org, devicetree-discuss-mnsaURCQ41sdnm+yROfE0A@public.gmane.org, David DeBonis List-Id: devicetree@vger.kernel.org --===============1129750363== Content-Class: urn:content-classes:message Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C9FDB1.B4F0087F" ------_=_NextPart_001_01C9FDB1.B4F0087F Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable My (limited) understanding from reading other posts is that there is alread= y a GPIO subsystem for handling such misc-GPIO things. To me the cost of gates for multiple GPIO cores is small compared to the sy= stem cost of having a separate OF binding. IMHO, this should be exposed the way any other GPIO= with such capabilities is on any other OF/device-tree enabled system. Steve -----Original Message----- From: John Williams [mailto:john.williams-g5w7nrANp4BDPfheJLI6IQ@public.gmane.org] Sent: Sun 7/5/2009 2:18 AM To: Stephen Neuendorffer Cc: michal.simek-g5w7nrANp4BDPfheJLI6IQ@public.gmane.org; John Linn; David DeBonis; devicetree-discus= s@ozlabs.org Subject: Re: Device tree BSP = On Sun, Jul 5, 2009 at 4:15 AM, Stephen Neuendorffer < stephen.neuendorffer-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org> wrote: > > > I'm not exactly sure what you're trying to do here, but it doesn't look > right to me. > In particular, why would I have to have a separate core for these > functions? > Furthermore, I'm sure there must be some generic mechanisms that can/shou= ld > be used for these kind of things. > In general, we shouldn't reinvent the wheel here.. > The issue as I see it is that in a hardware design, the GPIO is a very convenient core to drive a heartbeat LED, and aux input on proc_sys_reset (for software-driven reset), or whatever. Clearly you don't want these GPIO cores to enumerate as regular xps_gpio devices, binding to the standard GPIO driver and appearing in /dev/gpioN Is your concern the manual override of OF_ binding (the "compatible" strings), or just the HW overhead of an extra core to drive these HW utilit= y functions? Save us from the bad old days of "misc_logic" IP cores that drove this stuff in older Xilinx reference designs! Would you propose to get tricky and allocate specific bits on existing GPIO= s for these "special" functions, and write the GPIO driver/framework to mask off these bits etc? Seems like a complicated software solution to a proble= m trivially solved with a few extra gates. Cheers, John -- = John Williams, PhD, B.Eng, B.IT PetaLogix - Linux Solutions for a Reconfigurable World w: www.petalogix.com p: +61-7-30090663 f: +61-7-30090663 This email and any attachments are intended for the sole use of the named r= ecipient(s) and contain(s) confidential information that may be proprietary= , privileged or copyrighted under applicable law. If you are not the intend= ed recipient, do not read, copy, or forward this email message or any attac= hments. Delete this email message and any attachments immediately. ------_=_NextPart_001_01C9FDB1.B4F0087F Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable RE: Device tree BSP

My (limited) understanding from reading other posts is th= at there is already a GPIO subsystem for handling such misc-GPIO things. To me the cost of gates for multiple GPIO cores is small compared to the sy= stem cost of having
a separate OF binding.  IMHO, this should be exposed the way any other= GPIO with such capabilities
is on any other OF/device-tree enabled system.

Steve

-----Original Message-----
From: John Williams [mailto:= john.williams-g5w7nrANp4BDPfheJLI6IQ@public.gmane.org]
Sent: Sun 7/5/2009 2:18 AM
To: Stephen Neuendorffer
Cc: michal.simek-g5w7nrANp4BDPfheJLI6IQ@public.gmane.org; John Linn; David DeBonis; devicetree-discus= s@ozlabs.org
Subject: Re: Device tree BSP

On Sun, Jul 5, 2009 at 4:15 AM, Stephen Neuendorffer <
stephen.neuendorffer-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org> wrote:

>
>
> I'm not exactly sure what you're trying to do here, but it doesn't loo= k
> right to me.
> In particular, why would I have to have a separate core for these
> functions?
> Furthermore, I'm sure there must be some generic mechanisms that can/s= hould
> be used for these kind of things.
> In general, we shouldn't reinvent the wheel here..
>

The issue as I see it is that in a hardware design, the GPIO is a very
convenient core to drive a heartbeat LED, and aux input on proc_sys_reset (for software-driven reset), or whatever.

Clearly you don't want these GPIO cores to enumerate as regular xps_gpio devices, binding to the standard GPIO driver and appearing in /dev/gpioN
Is your concern the manual override of OF_ binding (the "compatible&qu= ot;
strings), or just the HW overhead of an extra core to drive these HW utilit= y
functions?  Save us from the bad old days of "misc_logic"&nb= sp; IP cores that
drove this stuff in older Xilinx reference designs!

Would you propose to get tricky and allocate specific bits on existing GPIO= s
for these "special" functions, and write the GPIO driver/framewor= k to mask
off these bits etc?  Seems like a complicated software solution to a p= roblem
trivially solved with a few extra gates.

Cheers,

John
--
John Williams, PhD, B.Eng, B.IT
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com  p: +61-7-30090663  f: +61-7-30090663


This email and any attachments are intended for the sole u= se of the named recipient(s) and contain(s) confidential information that m= ay be proprietary, privileged or copyrighted under applicable law. If you a= re not the intended recipient, do not read, copy, or forward this email mes= sage or any attachments. Delete this email message and any attachments imme= diately. ------_=_NextPart_001_01C9FDB1.B4F0087F-- --===============1129750363== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ devicetree-discuss mailing list devicetree-discuss-mnsaURCQ41sdnm+yROfE0A@public.gmane.org https://ozlabs.org/mailman/listinfo/devicetree-discuss --===============1129750363==--