Re: [Patch v1 01/10] memory: tegra: add interconnect support for DRAM scaling in Tegra234

[Sumit Gupta]

On 21/12/22 22:13, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
>
>
> 21.12.2022 12:35, Sumit Gupta пишет:
> > On 20/12/22 23:40, Dmitry Osipenko wrote:
> > > External email: Use caution opening links or attachments
> > >
> > >
> > > 20.12.2022 19:02, Sumit Gupta пишет:
> > > > +static int tegra_emc_icc_get_init_bw(struct icc_node *node, u32
> > > > *avg, u32 *peak)
> > > > +{
> > > > +     *avg = 0;
> > > > +     *peak = 0;
> > > > +
> > > > +     return 0;
> > > > +}
> > >
> > > Looks wrong, you should add ICC support to all the drivers first and
> > > only then enable ICC. I think you added this init_bw() to work around
> > > the fact that ICC isn't supported by T234 drivers.
> >
> > If get_bw hook is not added then max freq is set due to 'INT_MAX' below.
> >
> >   void icc_node_add(struct icc_node *node, struct icc_provider *provider)
> >   {
> >     ....
> >     /* get the initial bandwidth values and sync them with hardware */
> >     if (provider->get_bw) {
> >           provider->get_bw(node, &node->init_avg, &node->init_peak);
> >     } else {
> >           node->init_avg = INT_MAX;
> >           node->init_peak = INT_MAX;
> >   }
> >
> > So, will have to add the empty functions at least.
> >
> >   static int tegra_emc_icc_get_init_bw(struct icc_node *node, u32 *avg,
> > u32 *peak)
> >   {
> > -       *avg = 0;
> > -       *peak = 0;
> > -
> >          return 0;
> >   }
> >
> > Support to all the client drivers can't be added at once as there are
> > many drivers all with different requirements and handling. This patch
> > series is the beginning to add the basic interconnect support in new
> > Tegra SoC's. Support for more clients will be added later one by one or
> > in batch.
>
> This means that bandwidth management isn't working properly. You should
> leave the freq to INT_MAX and fix the missing integer overflows in the
> code if any, or read out the BW from FW.
>
> Once you'll enable ICC for all drivers, it will start working.

Referred the below patches and now understand what you mean.

https://patchwork.kernel.org/project/linux-arm-msm/cover/20200825170152.6434-1-georgi.djakov@xxxxxxxxxx/
 https://lore.kernel.org/all/20210912183009.6400-1-digetx@xxxxxxxxx/

There is no MRQ currently in BPMP-FW to get the bandwidth for a client.
So, can't add that in get_bw(). As explained earlier, we are in process 
adding of adding support for all clients but that may take some time. We 
can remove the get_bw() calls initializing "*bw = 0" once we have the 
support added in all clients. Noticed that below drivers also do same.

 $ grep -rB3 "*peak = 0" drivers/interconnect/*
 drivers/interconnect/imx/imx.c-static int imx_icc_get_bw(struct 
icc_node *node, u32 *avg, u32 *peak)
 drivers/interconnect/imx/imx.c-{
 drivers/interconnect/imx/imx.c- *avg = 0;
 drivers/interconnect/imx/imx.c: *peak = 0;
 --
 drivers/interconnect/qcom/msm8974.c-static int msm8974_get_bw(struct 
icc_node *node, u32 *avg, u32 *peak)
 drivers/interconnect/qcom/msm8974.c-{
 drivers/interconnect/qcom/msm8974.c-    *avg = 0;
 drivers/interconnect/qcom/msm8974.c:    *peak = 0;